Non-conductor

from Wikipedia, the free encyclopedia

Non-conductors are substances whose electrical conductivity of less than 10 −8  S · cm −1 or a specific resistance of more than 10 8 Ω · cm is comparatively low and therefore mostly irrelevant and below that of semiconductors . While the term is used in physics for any material such as gases and the vacuum , in technology it usually only means solids .

Other partly synonymous terms are insulator, insulating material and dielectric . In addition to the material property described here, the term insulator also means the non-conductive component that is used to fasten electrical components, see insulator . If non-conductors are used to isolate electrical conductors such as cables , they are called insulating materials. If the insulating materials determine the electrical properties of electrical or electronic components (e.g. capacitors or coaxial cables ), they are referred to as dielectric.

Subdivision

Ideal non-conductors do not conduct electrical current, they have an infinitely high resistance and no free moving charge carriers, which means that their conductivity is zero. However, there are no ideal dielectrics (since the perfect vacuum does not exist in nature either, the properties of the ideal dielectric could only be approximated in a few experiments. See also insulating material: supra-insulator effect ). Real non-conductors, however, always have a weak conductivity, depending on the temperature, and thus a finite specific resistance. Yet they can often be treated like ideal dielectrics and their conductivity can be neglected.

Physical Properties

Non-conductors are substances whose majority of charge carriers such as electrons are firmly bound to the atoms or whose ions are firmly built into the crystal lattice and therefore have no significant mobility . This includes most non-metals as well as hydrocarbons and many other organic compounds . Due to the variety of non-conductive materials, a general description of the physical properties other than electrical conductivity is not possible.

Band structures of non-conductors (middle) and semiconductors (right)

As described, materials with a conductivity in the range 10 −8 to more than 10 −26  S · cm −1 belong to the group of non-conductors. This value is due to the very low density of free electrical charge carriers (electrons and / or ions). Using the example of a non-conductive solid such as a diamond, this can best be illustrated using the energy band model. In the case of non-conductors, the valence band is fully occupied. Since the “ forbidden zone ” (energy gap between the valence and conduction band ) is very large ( E G > 3 eV), electrons can hardly change into the conduction band by simple thermal excitation (at room temperature or under normal conditions). Their low conductivity is therefore mainly due to ions. This is comparatively seldom the case even at greatly increased temperatures, at which the mean energy of the electrons would theoretically be sufficient to switch to the conduction band. It is more likely that ionization processes occur beforehand, contamination leads to loss effects, or the material is destroyed by the thermal load. In this respect, non-conductors differ from semiconductors . Semiconductors also have a “forbidden zone”, but this is sufficiently small that many electrons can be excited from the valence band into the conduction band even at low temperatures and are thus available for charge transport without damaging the semiconductor. The border area between non-conductors and semiconductors lies at an approximate energy gap of three electron volts .

Only a very small number of particles can move freely and form so-called leakage currents.

The number of freely movable charge carriers increases both with increasing temperature ((strong) heating) and with increasing voltage (field strength).

Therefore, all as a "non-conductor" labeled substances or materials may despite their designation with enough energy , for example in (very) high temperature or a high enough voltage for by applying guided by (higher or high) electrical currents are brought, whereby these transform themselves into electrical conductors , but often only for a short time, since solids in particular are often irreversibly destroyed. See: Isolator: Overload Damage .

Thus, apart from the application of a very high voltage, diamond also becomes a conductor when it is red hot , as does glass, which then melts.

Examples

Diamond - a non-conductor

Many substances are non-conductors, one of the best-known representatives is pure carbon in the diamond modification . However, numerous carbon compounds also count as non-conductors, for example amber or various plastics . The latter are used, among other things, for the insulation of cables or for housings. Other non-conductors are ceramic materials , glass or even silicones .

Non-ionized, dry gases such as argon , oxygen or normal dry air are also non-conductors. In general, the presence of water is responsible for many natural substances or mixtures of substances (e.g. wood ) that do not conduct electricity significantly on their own, so that they become conductors. Distilled or deionized water is considered an insulator, but since some water molecules are always dissociated , ions are available that conduct the electrical current and make water a poor insulator. With normal tap water or water in lakes, the dissolved salts (metal and non-metal ions) etc. are added. These increase the conductivity enormously and make water a conductor .

Salts in the solid state are - despite their ionic structure - mostly non-conductors. The binding forces between the ions are too great for enough ions to move freely. If salts are melted, this changes. The ions are no longer bound so tightly to their neighboring ions and so molten salts can transport the electrical current through ionic conduction .

Web links

Wiktionary: Non-conductor  - explanations of meanings, word origins, synonyms, translations

Individual evidence

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