Why is wood called non-metal
As Non-conductors In physics and technology, one denotes a substance that has no or practically insignificant electrical conductivity - approximate limit value: less than 10-10S cm-1 - owns.
Other common names for non-conductors are, depending on the area of application, insulator and dielectric. It should be noted that the term insulator, in addition to the material properties described here, also refers to an insulating component, see insulator. If non-conductors are used to insulate electrical conductors, 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.
Non-conductors are substances whose electrons are firmly bound to the atoms or whose ions are firmly built into the crystal lattice. 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.
As described, materials with a conductivity in the range 10-10–10-18S cm-1 counted 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 valence and conduction band) is very large (E.G> 3 eV), no electrons can change into the conduction band due to thermal excitation. This does not occur 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, 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 electrons can be excited from the valence band into the conduction band even at low temperatures and are thus available for charge transport. The border area between non-conductors and semiconductors lies at an approximate energy gap of three electron volts.
There are innumerable examples of non-conductors, one of the most famous representatives is probably carbon in the form of diamond or amber. In general, there are many organic materials that are non-conductors. Various plastics are used for the insulation of cables or for housings. Other non-conductors are various 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 for many natural substances or mixtures of substances (e.g. wood, which does not conduct electricity by itself, is responsible for the fact that these become conductive, because distilled or deionized water is considered an insulator, but always there) Some water molecules are dissociated, ions are available that conduct the electrical current and make water a poor insulator. In normal tap water or water in lakes, the dissolved salts (metal and non-metal ions) etc. are added, they increase the conductivity and make water a ladder.
By the way, salts in the solid state are mostly non-conductors despite their ionic structure. The binding forces between the ions are too great for individual 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.
Category: Electrotechnical material
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