Crystals are solid bodies with a regular geometric shape. The structure within which ordered particles are located is called a crystal lattice. The points of location of the particles in which they oscillate are called the nodes of the crystal lattice. All these bodies are divided into monocrystals and polycrystals.
What are single crystals
Single crystals are single crystals, in which the crystal lattice has a clear order. Often a single crystal has a regular shape, but this feature is not mandatory when determining the type of crystal. Most minerals are single crystals.
The external form depends on the growth rate of the substance. With a slow increase and uniformity of the material, the crystals have the correct cut. At medium speed, the cut is not pronounced. At a high crystallization rate, polycrystals consisting of many single crystals grow.
Classic examples of single crystals are diamond, quartz,topaz. In electronics, single crystals, which have the properties of semiconductors and dielectrics, are of particular importance. Alloys of single crystals are characterized by increased hardness. Ultrapure single crystals have the same properties regardless of origin. The chemical composition of minerals depends on the growth rate. The slower the crystal grows, the more perfect its composition.
Polycrystals
Single crystals and polycrystals are characterized by high molecular interaction. A polycrystal consists of many single crystals and has an irregular shape. They are sometimes called crystallites. They appear as a result of natural growth or are grown artificially. Polycrystals can be alloys, metals, ceramics. The main characteristics are made up of the properties of single crystals, but grain sizes, the distance between them, and grain boundaries are of great importance. In the presence of boundaries, the physical characteristics of polycrystals change significantly, strength decreases.
Polycrystals are generated as a result of crystallization, changes in crystalline powders. These minerals are less stable than single crystals, resulting in uneven growth of individual grains.
Polymorphism
Single crystals are substances that can exist in two states at once, which will differ in their physical properties. This feature is called polymorphism.
At the same time, a substance in one state can be more stable than another. When environmental conditions change, the situation maychange.
Polymorphism is of the following types:
- Reconstruction - decay occurs to atoms and molecules.
- Deformation - the structure is modified. Compression or stretching occurs.
- Shift - some elements of the structure change their location.
Crystal properties can change with a sudden change in composition. The classic example of polymorphism is carbon modification. In one state it is diamond, in another it is graphite, substances with different properties.
Some forms of carbohydrate turn into graphite when heated. Changes in properties can occur without deformation of the crystal lattice. In the case of iron, the substitution of some components leads to the disappearance of magnetic properties.
Crystal strength
Any material used in modern technology has a final strength. An alloy of nickel, chromium and iron has the greatest strength. Increasing the strength of metals will improve military and civilian equipment. Increased wear resistance will result in longer service life. For this reason, scientists have been studying the strength of single crystals for a long time.
Pure single crystals are crystals with an ideal crystal lattice, contain a small number of defects. With a decrease in the number of defects, the strength of metals increases several times. At the same time, the density of the metal remains almost the same.
Single crystals with an ideal lattice are resistant to mechanical stress up to the melting point. Do not change withtime. Most often, such single crystals have a zero dislocation. But this is an optional condition. Strength is explained by the fact that microcracks are formed in places where there is the greatest number of dislocations. And in their absence, there is nowhere for cracks to appear. This means that the single crystal will last until the threshold of its strength is exceeded.
Artificial single crystals
Growing single crystals is possible at the current level of science. When processing metal, without changing its composition, you can create a single crystal that has a high margin of safety.
There are 2 known methods for the production of single crystals:
- super high pressure and metal casting;
- cryogenic pressure.
The first method is popular for processing light metals. Given the purity of the metal and increasing pressure, a new metal will gradually appear that has the same properties, but with increased strength. Under certain conditions, it is possible to obtain a single crystal with an ideal lattice. In the presence of impurities, there is a possibility that the crystal lattice will not be ideal.
In heavy metals, with increasing pressure, the process of changing the structure occurs. The single crystal has not turned out yet, but the substance has changed properties.
Cryogenic casting is based on the production of cryogenic liquids. Crystallization does not occur under the influence of a magnetic field. The semi-crystalline form becomes a crystal after being electrically charged.
Diamondand quartz
Diamond properties are based on the fact that it is a substance with an atomic crystal lattice. The bond between atoms determines the strength of a diamond. Under constant conditions, the diamond does not change. When exposed to a vacuum, it gradually turns into graphite.
Crystal sizes vary significantly. Synthetically grown diamonds have cube faces and look different from their counterparts. The properties of diamond are used to cut glass.
Quartz crystals are found everywhere. The mineral is one of the most common. Quartz is usually colorless. If there are many cracks inside the stone, then it is white. When other impurities are added, it changes color.
Quartz crystals are used in the production of glass, to create ultrasound, in electrical, radio, television equipment. Some varieties are used in jewelry.
Structure of single crystals
Metals in the solid state have a crystalline structure. The structure of single crystals is an endless series of alternating atoms. In reality, the ordering of atoms can be disturbed due to thermal effects, mechanical or for a number of other reasons.
Crystal lattices are found in 3 types:
- tungsten type;
- copper type;
- magnesium type.
Application
Artificial single crystals is an opportunity to obtain material with new properties. The application area of single crystals is very large. Quartz and spar were created by nature, while sodium fluoride was artificially grown.
Monocrystals arematerials used in optics and electronics. Quartz and mica are used in optics but are expensive. Under artificial conditions, you can grow a single crystal, which will be distinguished by purity and strength.
Diamond is used where high strength is required. But it is successfully synthesized in artificial conditions. Three-dimensional single crystals are grown from melts.
