Static electricity

from Wikipedia, the free encyclopedia
This article or the following section is not adequately provided with supporting documents ( e.g. individual evidence ). Information without sufficient evidence could be removed soon. Please help Wikipedia by researching the information and including good evidence.

The static electricity is a special case of contact electricity . It is said to have been around 550 BC. B.C. by Thales of Miletus on amber . This is due to the energetically favorable transition of electrons between two contacting materials due to the difference in the work function . Electrons are transferred until the resulting potential difference (contact voltage) compensates for the energy gain .

The friction ensures an effective expression of the touch electricity, because the latter requires molecular distances that are limited to only the smallest proportions of the apparent contact surface with normal substances. By rubbing, a sufficient approximation of the fabrics is temporarily achieved for significantly larger areas of the actual surface. For the actual effect of the charge separation between the different materials, however, the process of friction does not play a role.

history

The body became electrically charged through contact with plastic and the hair repelled each other.

William Gilbert introduced the description of electricity with his investigations into vis electrica (he also used this word) . He was the first to make a clear distinction between magnetism and static electricity; he investigated the electrical charge on many substances (not only on the amber that gave it its name).

Otto von Guericke , Charles du Fay , Benjamin Franklin and many others carried out experiments on the nature of electrical charge in the 17th and 18th centuries . In experiments with a glass tube that is electrostatically charged by friction, Benjamin Franklin spoke of “ a type of charge” that only changes its location and thus causes positive or negative charging. Jean-Antoine Nollet and others advocated the so-called " two- fluid theory" , according to which electrified bodies are surrounded by two types of electricity, the effluvium and the affluvium .

The terms “glass-like” electricity and “resin- like” electricity coined by du Fay are derived from the behavior of these materials when charged by friction, substances made of glass have opposite properties to those of resin-like or amber-like substances. Franklin is based on the convention that glass-like electricity stands for the positive and resin-like electricity for the negative sign.

Examples

Well-known examples of experiments with static electricity are: amber / wool or polystyrene / synthetic textiles .

Charging by static electricity also leads to voltages (potential differences)

  • when combing between a comb and - especially freshly washed, dry - hair,
  • when walking in rooms with carpeting between this and the shoe soles, i.e. the person wearing the shoes and the earth,
  • when rolling with chair castors, inline skates also on clean, dry plastic and ceramic floors,
  • between items of clothing and between clothing and textile-covered seats (e.g. car seats),
  • between the plastic cover and the paper goods packed with it - especially important for light-sensitive photo paper,
  • when pulling an adhesive strip from the roll between adhesive and tape - it tends to clap again.

hazards

Charges caused by friction are usually harmless in the aforementioned cases, but they lead to electrostatic discharges that can damage electronic devices and components (see ESD ). Spark discharges can ignite highly flammable substances in the immediate vicinity, which can lead to serious accidents, for example at petrol stations or in the presence of flour dust.

On certain machines (paper and film production), frictional electricity generates such high voltages and energies that there is a risk of fire and a dangerous electric shock .

When filling up with non-conductive, flammable liquids, the moment when the filler neck and filler fitting come close for the first time or are separated. When filling balloons with hydrogen .

Triboelectric effect

The triboelectric effect describes the electrical charging of two materials through contact with one another and subsequent separation. A generally recognized justification for this effect can only be found through modern solid-state physics .

The mere contact is decisive for the charging of two materials. This requires a different work function of the materials. This can also involve two identical materials, the Fermi levels of which are only shifted by moisture or contamination on or in the material.

The term triboelectric effect originally comes from the Greek term tribein = to rub . The choice of term is based on an error in the discovery of the effect by the Greeks over 2000 years ago when an amber was rubbed with a cat's skin .

Triboelectric series

The triboelectric series indicates the electron affinity of a material. The further a material is at the positive end of the series, the more electrons it will give up when touched or rubbing against a material that is further at the negative end of the series. The actual quantity of charge separation due to the triboelectric effect depends on other factors such as temperature , surface properties , electrical conductivity and water absorption .

Positive end of the series (+)  Asbestos , glass , nylon , wool , lead , silk , aluminum , paper , cotton , steel , hard rubber , nickel / copper , brass / silver , synthetic  rubber , Orlon , Saran , polyethylene , Teflon  (PTFE) , Silicone rubber  (-) negative end of the series

Utility applications

The static electricity is the functional principle of the electrifying machines and is used in belt generators . Another important application is the use in sorting mineral grains or different plastics from one another. The particles are charged differently (positively or negatively) through mutual contact and then z. B. separated from each other when falling by an electrical high voltage field.

Textile and carpet brushes transport dust and fibers well into the storage chamber if the transport is supported by electrical attraction and repulsion.

In total darkness, for example due to a power failure, imprisonment, play, removing a woolen or plastic sweater over your head can generate so many sparks that a closer environment is illuminated just enough to allow orientation. Increasingly, however textiles are as conductive fitted that this radio drag is reduced.

Avoidance

Static electricity is avoided by discharging the resulting charges (see article Electrostatic discharge ).

Effective methods for this are:

  • Antistatic spray (creates a weakly conductive surface)
  • Antistatic packaging (weakly conductive materials or metal foils, threads, graphite layers)
  • Antistatic clothing (treated textiles or incorporated metal threads)
  • Antistatic tool handles (weakly conductive plastics)
  • Air humidification (acts by increasing the water content and thus making surfaces conductive, including their accumulation of dirt and dust)
  • Ionizing the air (see ionizer )
  • Grounding of all parts, tools and the human body (ESD workplace)
  • Connect all external connections of an IC so that no potential difference can arise between them, for example by inserting them into conductive foam
  • Earthing of tank trucks by means of rubber-copper braided tape that touches the roadway and earthing clamp with cable before each refueling process, conductive tank hose.

Web links

Individual evidence

  1. ↑ Kurt Sattelberg: From electron to electronics. 2nd Edition. Aarau 1982, p. 24.
  2. ^ Walter J. Moore, Dieter O. Hummel: Physikalische Chemie. de Gruyter Verlag, Berlin 1976, p. 498.
  3. ↑ Jürgen Teichmann: On the history of electrostatics. From the first beginnings to 1800. ( Memento from February 4, 2015 in the Internet Archive ) In: Teaching Physics. 10, 1999, p. 54 ff. (PDF; 142 kB)
  4. ↑ Duden, German Universal Dictionary. See etymology under the entry Tribology