How do electrostatic charges arise?

Creation of electrostatic charge

In their natural state, bodies have balanced amounts of positive and negative charges. This makes them electrically inert and they do not interact with their surroundings. However, as a result of various phenomena, these charges can move, resulting in electrified surfaces. The principle of conservation of charge states that in an isolated system, the total charge does not change - it can only move between bodies. The unit of charge is the coulomb (C) and the fundamental charge is that of the electron: 1,602 × 10^-19 C.

Electrification by contact

• Load transfer on contact

  During contact between two bodies, electrons can flow. As a result, one body acquires an excess of electrons (negative charge) and the other a deficiency (positive charge). A so-called double layer of charges is created.

• Potential difference between metals

  When two metals come close together, a so-called tunnel effect can occur - electrons flow from the metal with a lower exit work to the one with a higher one. A potential difference is created and the metals electrify with opposite signs according to the Volta series.

• Metal to semiconductor or insulator contact

  In semiconductors and insulators, electron flow depends on the type of material, the presence of dopants and the surface structure. Electron transfer can occur between a metal and an insulator and the sign of the charge depends on many factors.

• Contact between non-conductive bodies

  According to Lenard's hypothesis, solids can have a negatively charged surface layer. Bodies with a higher dielectric constant give up electrons more easily, becoming positive. A so-called tri-electric series is then formed, but its order is not fixed and depends on the experimental conditions.

Electrification by friction

Friction increases the number of contact points and temperature, which promotes the formation of electrostatic charges. This type of electrification, known as triboelectrification, can even occur between identical materials. Charges are also created when powders are impacted, granules are transferred or friction is applied to air.

Electrification by induction

If a conducting body is placed in the vicinity of an electric field, the internal charges shift - some gather on one side, others on the other. Once the conductor is removed from the field and separated, charges can remain on parts of the conductor. In insulators, this process can take many hours.

Fleet electrification

High voltages applied to the electrodes can cause so-called fugitive discharges, or silent discharges in the gas. These produce ions that accumulate on nearby surfaces - especially non-conductive ones - creating electrostatic charges.

Electrification of liquids

When a liquid flows through pipes, overflows or splashes, charge separation can occur at the interface. If the liquid conducts well, the charges quickly equalise. If this is not the case, they can accumulate on the walls, obstructions or ends of the pipes.

Electrification during solidification

When liquids with molecules possessing a dipole moment are frozen, an ordering of the dipoles takes place, which is similar to charge separation. Ions from the solution build into the crystal lattice, causing the resulting crystals to become electrified.

Piezo electrification

In some materials, under mechanical pressure, an electrical polarisation is created. A shift of positive and negative charges occurs, resulting in a charge on the surface of the material.

Summary

Electrostatic charges can be created in many different ways: by contact, friction, induction, field action, fluid flow or mechanical deformation. Although these mechanisms differ, they have one thing in common - they always involve the displacement of already existing charges, rather than creating them from nothing. Understanding these phenomena is of great importance in many fields - from industry to the life sciences.