Is wood a conductor of electricity? Electrical properties of wood

In electricity, there are three main groups of materials - these are conductors, semiconductors and dielectrics. Their main difference is the ability to conduct current. In this article, we will look at how these types of materials differ and how they behave in an electric field.

What is a conductor

A substance in which there are free charge carriers is called a conductor. The movement of free carriers is called thermal. The main characteristic of a conductor is its resistance (R) or conductivity (G) - the reciprocal of resistance.

talking in simple terms- A conductor conducts current.

Metals can be attributed to such substances, but if we talk about non-metals, then, for example, carbon is an excellent conductor, it has found application in sliding contacts, for example, motor brushes. Wet soil, solutions of salts and acids in water, the human body also conduct current, but their electrical conductivity is often less than that of copper or aluminum, for example.

Metals are excellent conductors due to a large number free charge carriers in their structure. Under influence electric field charges begin to move, as well as redistribute, the phenomenon of electrostatic induction is observed.

What is a dielectric

Dielectrics are substances that do not conduct current, or conduct, but very poorly. There are no free charge carriers in them, because the bond of the particles of an atom is strong enough to form free carriers, therefore, under the influence of an electric field, no current arises in the dielectric.

Gas, glass, ceramics, porcelain, some resins, textolite, carbolite, distilled water, dry wood, rubber are dielectrics and do not conduct electricity. In everyday life, dielectrics are found everywhere, for example, electrical appliances, electrical switches, plugs, sockets, and so on are made from them. In power lines, insulators are made of dielectrics.

However, if there are certain factors, such as elevated level humidity, electric field strength above the permissible value, and so on - lead to the fact that the material begins to lose its dielectric functions and becomes a conductor. Sometimes you can hear phrases like "breakdown of the insulator" - this is the phenomenon described above.

In short, the main properties of a dielectric in the field of electricity are electrical insulating. It is the ability to prevent the flow of current that protects a person from electrical injuries and other troubles. The main characteristic of a dielectric is dielectric strength - a value equal to its breakdown voltage.

What is a semiconductor

A semiconductor conducts electric current, but not like metals, but subject to certain conditions- communication of energy to the substance in the required quantities. This is due to the fact that there are too few free charge carriers (holes and electrons) or they do not exist at all, but if you apply some amount of energy, they will appear. Energy can be of various forms - electrical, thermal. Also, free holes and electrons in a semiconductor can appear under the influence of radiation, for example, in the UV spectrum.

Where are semiconductors used? Transistors, thyristors, diodes, microcircuits, LEDs, etc. are made from them. Such materials include silicon, germanium, mixtures of different materials, such as gallium arsenide, selenium, arsenic.

To understand why a semiconductor conducts electricity, but not like metals, we need to consider these materials from the point of view of band theory.

Zone theory

The band theory describes the presence or absence of free charge carriers, relative to certain energy layers. The energy level or layer is the amount of energy of electrons (nuclei of atoms, molecules - simple particles), they are measured in the value of Electronvolts (EV).

The image below shows three types of materials with their energy levels:

Please note that the conductor energy levels from the valence band to the conduction band are combined into a continuous diagram. The conduction band and valence band overlap each other, this is called the overlap band. Depending on the presence of an electric field (voltage), temperature and other factors, the number of electrons may vary. Thanks to the above, electrons can move in conductors, even if you tell them some minimal amount energy.

A semiconductor has a certain band gap between the valence band and the conduction band. The band gap describes how much energy must be imparted to a semiconductor in order for current to begin to flow.

For a dielectric, the diagram is similar to the one that describes semiconductors, but the difference is only in the band gap - it is many times larger here. Differences due internal structure and substances.

We have reviewed the main three types of materials and given their examples and features. Their main difference is the ability to conduct current. Therefore, each of them has found its own scope: conductors are used to transmit electricity, dielectrics - to isolate current-carrying parts, semiconductors - for electronics. We hope that the information provided has helped you understand what conductors, semiconductors and dielectrics are in an electric field, as well as how they differ from each other.

The ability to conduct electric current characterizes the electrical resistance of wood. In general, the impedance of a wood sample placed between two electrodes is defined as the resultant of two resistances: volume and surface. The volume resistance numerically characterizes the obstacle to the passage of current through the thickness of the sample, and the surface resistance determines the obstacle to the passage of current along the surface of the sample. Indicators of electrical resistance are specific volume and surface resistance. The first of these indicators has the dimension of ohm per centimeter (ohm x cm) and is numerically equal to the resistance when current passes through two opposite faces of a 1X1X1 cm cube made of a given material (wood). The second indicator is measured in ohms and is numerically equal to the resistance of a square of any size on the surface of a wood sample when current is applied to the electrodes that limit two opposite sides of this square. The electrical conductivity depends on the type of wood and the direction of current flow. As an illustration of the order of magnitude of volume and surface resistance in table. some data is given.

comparative data on the specific volume and surface resistance of wood

To characterize the electrical conductivity, the volume resistivity is of the greatest importance. The resistance is highly dependent on the moisture content of the wood. As the moisture content of the wood increases, the resistance decreases. A particularly sharp decrease in resistance is observed with an increase in the content of bound moisture from an absolutely dry state to the limit of hygroscopicity. In this case, the specific volume resistance decreases millions of times. A further increase in humidity causes a drop in resistance only tenfold. This is illustrated by the data in Table.

specific volume resistance of wood in a completely dry state

Breed	Specific volume resistance, ohm x cm
	across the fibers	along the fibers
Pine	2.3 x 10 15	1.8 x 10 15
Spruce	7.6 x 10 16	3.8 x 10 16
Ash	3.3 x 10 16	3.8 x 10 15
Hornbeam	8.0 x 10 16	1.3 x 10 15
Maple	6.6 x 10 17	3.3 x 10 17
Birch	5.1 x 10 16	2.3 x 10 16
Alder	1.0 x 10 17	9.6 x 10 15
Linden	1.5 x 10 16	6.4 x 10 15
Aspen	1.7 x 10 16	8.0 x 10 15

influence of humidity on the electrical resistance of wood

The surface resistance of wood also decreases significantly with increasing humidity. An increase in temperature leads to a decrease in the volumetric resistance of wood. Thus, the resistance of false wood wood with an increase in temperature from 22-23 ° to 44-45 ° C (approximately twice) drops by 2.5 times, and beech wood with an increase in temperature from 20-21 ° to 50 ° C - 3 times. At negative temperatures, the volume resistance of wood increases. The specific volume resistance along the fibers of birch samples with a moisture content of 76% at a temperature of 0 ° C was 1.2 x 10 7 ohm cm, and when cooled to a temperature of -24 ° C, it turned out to be 1.02 x 10 8 ohm cm. Impregnation of wood with mineral antiseptics (for example, zinc chloride) reduces the resistivity, while impregnation with creosote has little effect on electrical conductivity. The electrical conductivity of wood is practical value when it is used for communication poles, high-voltage transmission line masts, power tool handles, etc. In addition, the electrical moisture meters are based on the dependence of electrical conductivity on wood moisture content.

electric strength of wood

Electrical strength is important when evaluating wood as an electrically insulating material and is characterized by a breakdown voltage in volts per 1 cm of material thickness. The electrical strength of wood is low and depends on the species, humidity, temperature and direction. With increasing humidity and temperature, it decreases; along the fibers it is much lower than across. Data on the electrical strength of wood along and across the fibers are given in table.

electrical strength of wood along and across the fibers

With a moisture content of pine wood of 10%, the following electrical strength was obtained in kilovolts per 1 cm of thickness: along the fibers 16.8; in the radial direction 59.1; in the tangential direction 77.3 (the determination was made on samples 3 mm thick). As you can see, the electrical strength of wood along the fibers is about 3.5 times less than across the fibers; in the radial direction, the strength is less than in the tangential direction, since the core rays reduce the breakdown voltage. Increasing the humidity from 8 to 15% (by a factor of two) reduces the dielectric strength across the fibers by about 3 times (average for beech, birch and alder).

The electrical strength (in kilovolts per 1 cm of thickness) of other materials is as follows: mica 1500, glass 300, bakelite 200, paraffin 150, transformer oil 100, porcelain 100. In order to increase the electrical strength of wood and reduce electrical conductivity when used in the electrical industry as an insulator it is impregnated with drying oil, transformer oil, paraffin, artificial resins; The effectiveness of such impregnation is evident from the following data on birch wood: impregnation with drying oil increases the breakdown voltage along the fibers by 30%, with transformer oil - by 80%, with paraffin - almost twice as compared with the breakdown voltage for air-dry unimpregnated wood.

dielectric properties of wood

The value showing how many times the capacitance of the capacitor increases if the air gap between the plates is replaced by a gasket of the same thickness from a given material is called the dielectric constant of this material. Dielectric constant (dielectric constant) for some materials is given in table.

permittivity of some materials

Material		Wood	The dielectric constant
Air	1,00	Spruce dry: along the fibers	3,06
		in the tangential direction	1,98
Paraffin	2,00
		in the radial direction	1,91
Porcelain	5,73
Mica	7,1-7,7	Beech dry: along the grain	3,18
		in the tangential direction	2,20
Marble	8,34
		in the radial direction	2,40
Water	80,1

Data for wood show a noticeable difference between the dielectric constant along and across the fibers; at the same time, the permittivity across the fibers in the radial and tangential directions differs little. The dielectric constant in a high frequency field depends on the frequency of the current and the moisture content of the wood. With increasing current frequency, the dielectric constant of beech wood along the fibers at a moisture content of 0 to 12% decreases, which is especially noticeable for a moisture content of 12%. With an increase in the moisture content of beech wood, the dielectric constant along the fibers increases, which is especially noticeable at a lower current frequency.

In a high frequency field, the wood heats up; the reason for the heating is the Joule heat loss inside the dielectric, which occurs under the influence of an alternating electromagnetic field. This heating consumes a part of the input energy, the value of which is characterized by the loss tangent.

The loss tangent depends on the direction of the field with respect to the fibers: it is approximately twice as large along the fibers as across the fibers. Across the fibers in the radial and tangential directions, the loss tangent differs little. The dielectric loss tangent, like the dielectric constant, depends on the frequency of the current and the moisture content of the wood. So, for absolutely dry beech wood, the loss tangent along the fibers first increases with increasing frequency, reaches a maximum at a frequency of 10 7 Hz, after which it begins to decrease again. At the same time, at a humidity of 12%, the loss tangent drops sharply with increasing frequency, reaches a minimum at a frequency of 105 Hz, and then increases just as sharply.

maximum loss tangent for dry wood

With an increase in the moisture content of beech wood, the loss tangent along the fibers increases sharply at low (3 x 10 2 Hz) and high (10 9 Hz) frequencies and almost does not change at a frequency of 10 6 -10 7 Hz.

Through a comparative study of the dielectric properties of pine wood and cellulose, lignin and resin obtained from it, it was found that these properties are determined mainly by cellulose. Heating of wood in the field of high frequency currents is used in the processes of drying, impregnation and gluing.

piezoelectric properties of wood

Electric charges appear on the surface of some dielectrics under the action of mechanical stresses. This phenomenon associated with the polarization of the dielectric is called the direct piezoelectric effect. Piezoelectric properties were first discovered in crystals of quartz, tourmaline, Rochelle salt, etc. These materials also have an inverse piezoelectric effect, which consists in the fact that their dimensions change under the influence of an electric field. Plates made of these crystals are widely used as emitters and receivers in ultrasonic technology.

These phenomena are found not only in single crystals, but also in a number of other anisotropic solid materials called piezoelectric textures. Piezoelectric properties have also been found in wood. It was found that the main carrier of piezoelectric properties in wood is its oriented component - cellulose. The intensity of polarization of wood is proportional to the magnitude of mechanical stresses from the applied external forces; the proportionality factor is called the piezoelectric modulus. The quantitative study of the piezoelectric effect, therefore, is reduced to the determination of the values ​​of the piezoelectric moduli. Due to the anisotropy of the mechanical and piezoelectric properties of wood, these indicators depend on the direction of mechanical forces and the polarization vector.

The greatest piezoelectric effect is observed under compressive and tensile loads at an angle of 45° to the fibers. Mechanical stresses directed strictly along or across the fibers do not cause a piezoelectric effect in wood. In table. the values ​​of piezoelectric modules for some rocks are given. The maximum piezoelectric effect is observed in dry wood, with increasing humidity it decreases, and then completely disappears. So, already at a humidity of 6-8%, the magnitude of the piezoelectric effect is very small. With an increase in temperature to 100 ° C, the value of the piezoelectric modulus increases. With a small elastic deformation (high modulus of elasticity) of wood, the piezoelectric modulus decreases. The piezoelectric modulus also depends on a number of other factors; however, the orientation of the cellulose component of wood has the greatest influence on its value.

piezoelectric wood modules

Open phenomenon allows deeper study fine structure wood. Indicators of the piezoelectric effect can serve as quantitative characteristics cellulose orientations and are therefore very important for studying the anisotropy of natural wood and new wood materials with properties specified in certain directions.

All materials that exist in nature differ in their electrical properties. Thus, from the whole variety of physical substances, dielectric materials and conductors are distinguished into separate groups. electric current.

What are conductors?

A conductor is such a material, a feature of which is the presence of freely moving charged particles in the composition, which are distributed throughout the substance.

Substances conducting electric current are melts of metals and the metals themselves, undistilled water, salt solution, wet soil, the human body.

Metal is the best conductor of electricity. Also among non-metals there are good conductors, for example, carbon.

All natural conductors of electric current are characterized by two properties:

• resistance indicator;
• conductivity indicator.

Resistance arises due to the fact that electrons in motion experience a collision with atoms and ions, which are a kind of obstacle. That is why conductors are assigned the characteristic of electrical resistance. The reciprocal of resistance is electrical conductivity.

Electrical conductivity is a characteristic (ability) of a physical substance to conduct current. Therefore, the properties of a reliable conductor are low resistance to the flow of moving electrons and, consequently, high electrical conductivity. That is, the best conductor is characterized a big indicator conductivity.

For example cable products: copper cable has a higher electrical conductivity compared to aluminum.

What are dielectrics?

Dielectrics are physical substances, in which at low temperatures there are no electric charges. The composition of such substances includes only atoms of a neutral charge and molecules. The charges of a neutral atom are closely connected with each other, therefore they are deprived of the possibility of free movement throughout the substance.

Gas is the best dielectric. Other non-conductive materials are glass, porcelain, ceramics, as well as rubber, cardboard, dry wood, resins and plastics.

Dielectric objects are insulators whose properties are mainly dependent on the state ambient atmosphere. For example, at high humidity, some dielectric materials partially lose their properties.

Conductors and dielectrics are widely used in the field of electrical engineering to solve various problems.

For example, all cable and wire products are made of metals, usually copper or aluminum. The sheath of wires and cables is polymer, as well as the plugs of all electrical appliances. Polymers are excellent dielectrics that do not allow the passage of charged particles.

Silver, gold and platinum products are very good conductors. But their negative characteristic, which limits their use, is their very high cost.

Therefore, such substances are used in areas where quality is much more important than the price paid for it (defense industry and space).

Copper and aluminum products are also good conductors, while they are not so high cost. Consequently, the use of copper and aluminum wires is ubiquitous.

Tungsten and molybdenum conductors have less good properties, so they are used mainly in incandescent light bulbs and high temperature heating elements. Poor electrical conductivity can significantly disrupt the operation of the electrical circuit.

Dielectrics also differ in their characteristics and properties. For example, in some dielectric materials there are also free electrical charges, albeit in a small amount. Free charges arise due to thermal vibrations of electrons, i.e. However, an increase in temperature in some cases provokes the detachment of electrons from the nucleus, which reduces the insulating properties of the material. Some insulators are characterized by a large number of "torn off" electrons, which indicates poor insulating properties.

The best dielectric is a complete vacuum, which is very difficult to achieve on planet Earth.

Completely purified water also has high dielectric properties, but such does not even exist in reality. It is worth remembering that the presence of any impurities in the liquid endows it with the properties of a conductor.

The main criterion for the quality of any dielectric material is the degree of compliance with the functions assigned to it in a particular electrical circuit. For example, if the properties of the dielectric are such that current leakage is negligible and does not cause any damage to the operation of the circuit, then the dielectric is reliable.

What is a semiconductor?

An intermediate place between dielectrics and conductors is occupied by semiconductors. The main difference between conductors is the dependence of the degree of electrical conductivity on temperature and the amount of impurities in the composition. Moreover, the material has the characteristics of both a dielectric and a conductor.

With increasing temperature, the electrical conductivity of semiconductors increases, and the degree of resistance decreases. As the temperature decreases, the resistance tends to infinity. That is, when the temperature reaches zero, semiconductors begin to behave like insulators.

The semiconductors are silicon and germanium.

Electrical conductivity. The ability of wood to conduct electricity is inversely related to its electrical resistance.

The impedance of a wood sample placed between two electrodes is defined as the resultant of two resistances: volume and surface. Highest value to characterize the electrical conductivity of the material has the first type of resistance, an indicator of which is volume resistivity which has the dimension of Ohm cm and is numerically equal to the resistance when current passes through two opposite faces of a cube with dimensions of 1x1x1 cm of the published material (wood).

Wood belongs to dielectrics (10 8 -10 17 ohm cm). For it, methods for measuring the resistance of solid dielectrics at constant voltages are applicable. Taking into account the specifics of wood, these methods were used by TsNIIMOD in the development of GOST 18408-73.

Different breeds have different electrical conductivity, but in all breeds it is several times greater along the fibers than across the fibers.

As the moisture content of the wood increases, the resistance decreases. A particularly sharp decrease in resistance (by tens of millions of times) is observed with an increase in the content of bound water, i.e., during the transition from an absolutely dry state of wood to the saturation limit of cell walls Wbp. . A further increase in humidity causes a drop in resistance only by tens or hundreds of times. This explains the decrease in the accuracy of moisture determination by electric moisture meters in the region above W b.p. .

An increase in the temperature of wood leads to a decrease in its volumetric resistance. On average, it is considered that an increase in the temperature of wood for every 12 ° C causes a decrease in resistance by about half.

The electrical conductivity of wood is taken into account when wood is used for communication poles, masts of high-voltage transmission lines, power tool handles, etc.

Electrical strength. This is the name of the ability of wood to resist breakdown, i.e., a decrease in resistance at high voltages. To determine the electrical strength of wood at an alternating voltage with a frequency of 50 Hz, TsNIIMOD developed GOST 18407-73. An indicator of electrical strength is E pr - the ratio of breakdown voltage to the thickness of the material, kV / mm.

The electrical strength of absolutely dry wood along the fibers is 1.3-1.5 kV / mm, which is 4-7 times less than across the fibers. With increasing humidity, the electrical strength decreases markedly. According to BelTI, the strength decreases by 2 times when the humidity changes from 10 to 14%. The electrical strength of wood compared to other solid insulating materials is low (for glass E pr \u003d 30, for polyethylene - 40 kV / mm). To increase the electrical strength, wood is impregnated with paraffin, drying oil, artificial resins and other substances.

Dielectric Properties. Wood in an alternating electric field exhibits its dielectric properties, which are characterized by two indicators. The first of them - the relative permittivity ε - is numerically equal to the ratio of the capacitance of a capacitor with a wood gasket to the capacitance of a capacitor with an air gap between the electrodes. The second indicator - the tangent of the dielectric loss angle tan δ - determines the proportion of the input power that is absorbed by the wood and converted into heat.

The dielectric constant absolutely dry wood with increasing density increases. So, for balsa wood (ρ 0 \u003d 130 kg / m 3) the dielectric constant across the fibers in the frequency range 10-10 11 Hz is on average 1.3, and for hornbeam (ρ 0 \u003d 800 kg / m 3) - 2, 6. The permeability along the fibers is 1.4 times higher on average. With an increase in wood moisture, e increases, since for water the value of this indicator in the frequency range 10-10 11 Hz is 81-7.5. According to G. I. Torgovnikov, at a humidity of 10% and a temperature of 20 ° C for wood with a density of ρ 0 \u003d 500 kg / m 3 at a frequency of 10 4 Hz it is 4.2, at a frequency of 10 10 Hz - 2.0, and at humidity 60% - respectively equal to 65 and 6.6. An increase in temperature from -40 to 100 ° C for absolutely dry wood leads to a slight increase (about 1.3 times). Increasing the temperature of wet wood leads to a more significant increase.

Loss tangent also depends on the density of the wood. Across the fibers, tg δ at a density of ρ 0 = 500 kg / m 3 and room temperature in the frequency range of 10-10 5 Hz is 0.005-0.007, and at a density of ρ 0 = 800 kg / m 3 this figure is 0.007-0.025. Along the fibers tg δ is higher than across the fibers, on average 1.7 times. With increasing humidity, tg δ increases. The frequency dependences of this indicator are complex. So, for wood with a density ρ 0 = 500 kg / m 3 at a temperature of 20 ° C and a humidity of 80%, the value of tg δ at a frequency of 10 3 Hz reaches 74, at a frequency of 10 8 Hz it decreases to 0.2, and in the region of microwave frequencies (10 10 Hz) increases to 0.34. An increase in the temperature of absolutely dry wood causes a decrease in tg δ, but this indicator increases in the microwave region. For wet wood (W=25%), heating leads to a significant increase in tg δ, but in the microwave region it changes insignificantly.

With dielectric heating, the temperature rises simultaneously throughout the entire volume of wood. This method of heating is practical use in the processes of drying, gluing and impregnation of wood. Heating in the microwave field can be used for drying wood, for surface thawing of logs before debarking and sawing.

Piezoelectric Properties. On the surface of anisotropic plates of crystals (quartz, tourmaline, Rochelle salt), when stretched or compressed, electric charges appear: positive on one side and negative on the other. Electric charges arise under the action of mechanical forces, pressure, therefore this phenomenon is called direct piezoelectric effect(the word "piezo" means pressure). These materials also have an inverse piezoelectric effect - their dimensions change under the influence of an electric field. Plates made of these crystals are widely used as emitters and receivers in ultrasonic technology.

Studies by V. A. Bazhenov showed that wood containing an oriented component, cellulose, also has such properties. The greatest piezoelectric effect is observed when a compressive and tensile load is applied at an angle of 45° to the fibers. Loads directed strictly along or across the fibers do not cause this effect. The piezoelectric effect is especially noticeable in dry wood, with increasing humidity it decreases and already at a moisture content of 6-8% it almost completely disappears. As the temperature rises to 100 °C, the effect increases. The higher the modulus of elasticity of wood, the less its piezoelectric effect.

This phenomenon allows a deeper study of the fine structure of wood, to characterize the degree of anisotropy of natural wood and new wood materials. It is used in the development of non-destructive methods for quality control of wood.

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A dielectric is a material or substance that practically does not transmit electric current. Such conductivity is obtained due to a small number of electrons and ions. These particles are formed in a non-conductive material only when high temperature properties are achieved. About what a dielectric is and will be discussed in this article.

Description

Each electronic or radio conductor, semiconductor or charged dielectric passes an electric current through itself, but the peculiarity of the dielectric is that even at a high voltage over 550 V, a small current will flow in it. An electric current in a dielectric is the movement of charged particles in a certain direction (it can be positive or negative).

Types of currents

The electrical conductivity of dielectrics is based on:

• Absorption currents - a current that flows in a dielectric at a constant current until it reaches an equilibrium state, changing direction when it is turned on and energized and when it is turned off. With alternating current, the tension in the dielectric will be present in it all the time while it is in the action of an electric field.
• Electronic electrical conductivity - the movement of electrons under the influence of a field.
• Ionic electrical conductivity - is the movement of ions. It is found in electrolyte solutions - salts, acids, alkalis, as well as in many dielectrics.
• Molionic electrical conductivity is the movement of charged particles called molions. It is found in colloidal systems, emulsions and suspensions. The phenomenon of the movement of molions in an electric field is called electrophoresis.

Classified according to state of aggregation and chemical nature. The first are divided into solid, liquid, gaseous and solidifying. By chemical nature, they are divided into organic, inorganic and organoelement materials.

By state of aggregation:

• Electrical conductivity of gases. Gaseous substances have a rather low current conductivity. It can occur in the presence of free charged particles, which appears due to the influence of external and internal, electronic and ionic factors: X-ray radiation and radioactive species, collisions of molecules and charged particles, thermal factors.
• Electrical conductivity of a liquid dielectric. Dependence factors: molecular structure, temperature, impurities, the presence of large charges of electrons and ions. The electrical conductivity of liquid dielectrics largely depends on the presence of moisture and impurities. The conductivity of electricity of polar substances is created even with the help of a liquid with dissociated ions. When comparing polar and non-polar liquids, the former have a clear advantage in conductivity. If the liquid is cleaned of impurities, this will contribute to a decrease in its conductive properties. With an increase in conductivity and its temperature, a decrease in its viscosity occurs, leading to an increase in the mobility of ions.
• solid dielectrics. Their electrical conductivity is determined as the movement of charged dielectric particles and impurities. In strong electric current fields, electrical conductivity is revealed.

Physical properties of dielectrics

When the specific resistance of the material is less than 10-5 Ohm * m, they can be attributed to conductors. If more than 108 Ohm * m - to dielectrics. There are cases when the resistivity will be many times greater than the resistance of the conductor. In the interval 10-5-108 Ohm*m there is a semiconductor. Metallic material is an excellent conductor of electric current.

Of the entire periodic table, only 25 elements belong to non-metals, and 12 of them, possibly, will have semiconductor properties. But, of course, in addition to the substances of the table, there are many more alloys, compositions or chemical compounds with the property of a conductor, semiconductor or dielectric. Based on this, it is difficult to draw a certain line of values various substances with their resistance. For example, at a reduced temperature factor, a semiconductor will behave like a dielectric.

Application

The use of non-conductive materials is very extensive, as it is one of the most commonly used classes of electrical components. It became quite clear that they can be used due to their properties in an active and passive form.

In a passive form, the properties of dielectrics are used for use in electrical insulating material.

In active form, they are used in ferroelectrics, as well as in materials for emitters of laser technology.

Basic dielectrics

Common types include:

• Glass.
• Rubber.
• Oil.
• Asphalt.
• Porcelain.
• Quartz.
• Air.
• Diamond.
• Pure water.
• Plastic.

What is a liquid dielectric?

Polarization of this type occurs in the electric current field. Liquid non-conductive substances are used in engineering for pouring or impregnating materials. There are 3 classes of liquid dielectrics:

Petroleum oils are low viscosity and mostly non-polar. They are often used in high-voltage instruments: high-voltage water. is a non-polar dielectric. Cable oil has found application in the impregnation of insulating paper wires with a voltage of up to 40 kV, as well as metal-based coatings with a current of more than 120 kV. Transformer oil has a cleaner structure than capacitor oil. This type of dielectric is widely used in production, despite the high cost compared to analog substances and materials.

What is a synthetic dielectric? Currently, it is banned almost everywhere due to its high toxicity, as it is produced on the basis of chlorinated carbon. A liquid dielectric based on organic silicon is safe and environmentally friendly. This type does not cause metal rust and has the properties of low hygroscopicity. There is a liquefied dielectric containing an organofluorine compound, which is especially popular because of its incombustibility, thermal properties and oxidative stability.

And the last type is vegetable oils. They are weakly polar dielectrics, these include flaxseed, castor, tung, hemp. Castor oil is highly heated and is used in paper capacitors. The rest of the oils are evaporated. Evaporation in them is not caused by natural evaporation, but chemical reaction called polymerization. It is actively used in enamels and paints.

Conclusion

The article discussed in detail what a dielectric is. Various species and their properties have been mentioned. Of course, in order to understand the subtlety of their characteristics, you will have to study the section of physics about them in more depth.