Articles, facts, galleries

Electricians who work in design bureaus mainly deal with circuits. However, circuits are only a small part of electrical engineering. Circuits and calculations are only auxiliary means for building machines, generating electricity, distributing it, and converting it into other types of energy. Materials are the basis of electrical engineering.

The materials used in electrical engineering are varied. Some elements of the periodic table are used in electrical engineering in pure form, while others are included in various chemical compounds that are important for electrical engineering.

In the last century, electrical engineering was said to rest on the "three pillars": copper, iron, and carbon. Copper is used for windings, iron for cores, and carbon for brushes and arc lamps.
Nowadays, all elements of the periodic table are used in electrical engineering.

The first element of the periodic table is the lightest gas, hydrogen. Hydrogen cools powerful turbogenerators, fills thyratrons, and sparks gaps. Hydrogen furnaces anneal parts of vacuum tubes.
Helium follows hydrogen. Like other inert gases — neon, argon, krypton, xenon — it is used to fill various vacuum tubes. Glass tubes filled with neon glow with a crimson fire. They burn in advertising signs, at airfields, in lighthouses. Incandescent lamps filled with krypton are highly efficient and small in size. All alkaline and alkaline earth metals are used in vacuum tube production. Sodium, potassium, and cesium are used for photocells. Barium, calcium, and strontium in the form of oxides and pure metals are used to coat the cathodes of electron tubes.

The third group of the periodic table begins with boron, the compound used to make durable and refractory borosilicate glass. Such glass is used to make flasks for generator tubes and gastrons.
It is impossible to retell even the most important things about the element with which the fourth group of the periodic table begins — carbon. Carbon is also used in pure form: graphite electrodes for arc furnaces, heaters for resistance furnaces, membranes and powder for microphones, carbons for spotlights, grids and anodes for thyratrons, and powerful mercury rectifiers. Carbon compounds are also used to make numerous insulating materials. Hydrocarbons are used to make solid insulation, varnishes, and enamels.

Lighting lamps are filled with nitrogen, high-frequency capacitors are insulated with compressed nitrogen, and many nitrogen compounds are also used as insulating materials.
Oxygen is rarely used in pure form in electrical engineering structures, but it is part of all glasses and porcelain. Compounds of all halides are used in electrical engineering: fluorine, chlorine, bromine, and iodine. Precious metals are very important for electrical engineering structures: relay contacts, capacitor plates (ceramic, for example) are made of silver, and resonators and waveguides for centimeter waves are coated with silver. The previous chapter already mentioned the use of silver in printed circuits.

Mercury is an important electrical engineering material. Current converters are filled with vapor.
Thin layers of gold are applied to the grids of some lamps to reduce electron emission. Platinum wires, platinum tin, and platinum crucibles are used in many cases in electrothermy and for other purposes.

The last of the natural elements, the 92nd element uranium-1, is also used in special resistors that must reduce their electrical resistance with temperature. These are thermistors - starting and regulating resistances. It is difficult to name a material that would not be considered "electrical engineering building materials". Rarefied gas, penetrated by electron flows, is a glowing plasma. A cubic meter of this plasma weighs a tiny fraction of a gram, making it an important construction material for an electrician, no less important than steel and cast iron.

Vacuum tube engineers cut "sleeves" from this plasma in powerful converters, fill discharge chambers with it, and filter it through meshes. Detailed graphs and tables indicate which holes the plasma will leak through and which mesh it will get stuck in.
An electrician is interested in many properties of the construction materials he uses to create his structures. Like a mechanical engineer, he must know the mechanical strength of materials. Like a heat engineer, he must know the materials' thermal conductivity and fire resistance.
However, there are three specific electrical characteristics of all materials. We should start with
them.
Electrical engineering deals with the movement of electric charges, their accumulation, the excitation of magnetic forces, the propagation of electromagnetic waves, and the mutual transformations of electric and magnetic energy.

Different substances affect these processes differently. In the air and highly rarefied gases, electromagnetic oscillations of any frequency propagate at the same speed. This is the speed of light, 300,000 km/sec, the upper limit for the speeds of all possible natural processes. In all formulas, this speed is denoted by the letter c.

Many solid and liquid substances also transmit electromagnetic waves. These are substances in which the movement of electric charges is difficult. The same substances in which electric charges move freely are opaque to electromagnetic waves. Falling on such bodies, electromagnetic waves waste their energy on swinging charges and fade into a thin layer of matter.

But even in transparent media, in which charges are bound and firmly seated in their places, electromagnetic waves move differently than in air and rarefied gases. The wave propagation speed is lower here. The value showing how often this speed is less than c is called the refractive index n. It usually depends on the length of the electromagnetic wave. For a beam of yellow light, water has n = 1.33, crown glass n = 1.5, and diamond n = 2.4. This is a very high refractive index for light waves, which is why the light rays "play" on the diamond faces.

For centimeter radio waves used in radar, water has a refractive index of ≈9. The transparency of the refractive index and the wavelength depend on the wavelength. Many opaque materials to light waves transmit longer electromagnetic waves with little attenuation - these are porcelain, ebonite, and many resins.

In everyday language, the word "ray" refers to something thin without perceptible width or thickness. The concept of a ray is often associated with a geometric line.

But a physicist would define a ray differently. He will say that a beam is a flow of energy and waves. Such a flow can exist only when the dimensions of its cross-section are many times greater than the wavelength.

Visible light waves have a length of about half a micron. A light beam with a diameter of 1 millimeter can accommodate two thousand wavelengths. In radar, centimeter waves are used, and there, we can talk about a beam when the dimensions of its cross-section are measured in meters. In smaller equipment, the laws of geometric optics are not applicable; the beam concept here can give nothing for calculations.

For a current with a frequency of 50 Hz, the minimum beam cross-section is tens of thousands of kilometers. All the installations that low-frequency electricians work with have dimensions many times smaller than the length of an electromagnetic wave. There is no point in talking about beams of such waves. There is nowhere for a beam to form in such an installation.
In these cases, the concept of the refractive index n is inapplicable. Instead, they talk about the permittivity of the substance. It is approximately equal to the square of the refractive index. This value is denoted by the Greek letter epsilon ε.

It is possible to approach the definition of the value of ε without touching on waves and rays. In the space around electric charges, there are electric forces. These forces weaken if some solid or liquid substance replaces the rarefied gas. The permittivity shows how often the magnitude of electric forces decreases when the electric charge, previously in the gas, is surrounded by the substance of interest to us. The permittivity value equals several units for most electrical insulating materials used in electrical engineering. Paraffin has ε=2. Porcelain masses have ε=6. Mica, ebonite, and transformer oil permittivity are within these limits. Materials with higher values ​​of ε are often used to accumulate electrical energy in capacitors. For example, ceramic masses containing titanium dioxide have ε≈60. The permittivity also depends on the aggregate state of the substance. Ice has ε=3.1, and water ε=81. But water is generally not so simple; we will discuss it in the next paragraph.

There are substances with a much higher permittivity, such as Rochelle salt, which has ε of several thousand. Titanium-barium compounds - barium titanates - have ε of the same order. Soviet scientists are intensively studying these compounds. Many interesting applications in science and technology are expected.

The second letter in this paragraph's title is the Greek "mu" (μ). The movement of charges or electric lines of force is an electric current; it invariably generates a magnetic flux. The ratio of magnetic forces to the current that generated them characterizes the medium's magnetic permeability.

The permeability of air is usually considered to be one, and the value μ shows how many times the permeability of a given substance differs from the permeability of air. Finally, the third characteristic of substances is their ability to conduct electric charges. The Greek letter sigma (σ) usually denotes specific electrical conductivity.

An ideal insulator should have a sigma equal to zero, and a perfect conductor should have a sigma equal to infinity. The reciprocal value is often used. It is called specific electrical resistance. The standard designation for it is the letter rho (p).

Materials with the same strength in all directions are often used for mechanical structures. Well-made steel, for example. However, other materials, such as wood, hold a load well in one direction (along the grain) and have insignificant strength in the other (across the grain).
The same is true for the electrical properties of materials. Copper, for example, has the same conductivity in all directions. The permittivity is the same in all directions for paraffin, glass, and amber. Other materials behave differently. Crystals often have different conductivity and different permittivity along various axes.

Transformer steel, used for transformer cores, has different magnetic permeabilities in various directions.