Triboelectric effect

The frictional electrification is a special case of contact electricity. It has already been discovered around 550 BC Thales of Miletus to amber ( Greek " electron" ). This is based on the low-energy transition of electrons between two contacting materials due to the difference in the work function. There are going on as long as electrons to itself as a result anabolic potential difference ( contact voltage ) makes up for the energy gain.

History

With his study of vis electrica ( comes from him and the use of this word ) led William Gilbert, the description of the electricity one. He distinguished between first clear distinction between magnetism and static electricity, examined the electrical charge at many substances ( not only in the eponymous Bernstein).

Benjamin Franklin looked in his first experiments in electricity, the nature of the electric charge. In experiments with an electrostatically charged by friction glass tube ( so-called " glass-like " electricity), he noted, firstly, that in any closed system, the sum of the existing electrical charges remains constant ( principle of conservation of charge ). Franklin spoke of " a type of cargo ", which only changed their residence and thus causes a positive or negative charge. His discovery refuted the then accepted and advocated by Jean -Antoine Nollet two-liquid theory that electrified bodies are surrounded by two electricity varieties, the effluvium and the Affluvium. He sat on the other his findings in the so-called one- fluid theory and coined the terms "plus " and " minus ". He is based on the convention that vitreous electricity for the positive and the resinous electricity for the negative sign. The terms of glass- or resin -like derived from the behavior of these materials during charging by friction ( static electricity ), materials of glass have opposite properties as the resin- or amber- like substances. The friction provides an effective expression of the contact electricity, because the latter are necessary for molecular distances that are limited in normal materials only modest proportions of the apparent contact area. By rubbing a sufficient approximation of the substances is temporarily achieved for much larger areas of the real surface. For the actual effect of the charge separation between the different materials, however, the operation of the friction does not matter.

Examples

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

Charging by friction electricity leads among other things to voltages ( potential differences)

• When combing between hair and comb,
• When walking in rooms with carpeting between this and the soles of shoes, so the person's shoes bearing and earth,
• Between clothing and the garment, the fabric-covered seats (such as car seats).

Hazards

Damage caused by friction loads are indeed in the above cases usually not dangerous, but they give rise to electrostatic discharges that can damage electronic devices and components (see ESD). Spark discharges may flammables in the immediate vicinity inflame, 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 ) caused by static electricity such high voltages and energy that fire hazard and the risk of a dangerous electric shock.

The triboelectric effect

The triboelectric effect describes the electrical charging of two materials by contact with each other and then separating. A generally accepted explanation for this effect is found only by modern solid state physics.

Decisive for the charging of two materials is only the mere contact. This requires a different work function of the materials. It may be also two identical materials whose Fermi level is shifted only by moisture or contaminants on or in the material.

The term triboelectric effect originates from the Greek term tribein = rub. The choice of terms based on an error in the discovery of the effect over 2000 years ago by the Greeks, as was rubbed with cat fur, a Bernstein.

Triboelectric series

The triboelectric series indicates the electron affinity of a material. The farther is a material at the positive end of the series, the more electrons it will leave in contact or friction with a material which is more on the negative end of the series. However, the actual quantity of the charge separation by the triboelectric effect depends on other factors such as temperature, surface texture, electrical conductivity, water uptake.

Positive end of the row ( ) 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

Practical applications

The static electricity is the operating principle of the electrical machines, and is used in tape generators. Another important application is the use for the sorting of mineral grains or of different plastics from each other dar. The particles through mutual contact differs ( positively or negatively ) charged, and then, for example, separated from each other while falling through a high voltage electric field.

Avoidance

Static electricity is avoided by the resulting charges are derived ( see Article Electrostatic Discharge ).

Effective methods for this are:

• Anti-static spray ( produces a weakly conducting surface )
• Antistatic packaging (weakly conductive materials or metal foils, threads, graphite layers )
• Anti-static clothing (treated textiles or incorporated metal threads )
• Antistatic Tool handles (weakly conductive plastics )
• Humidification
• Ionizing the air (see ionizer )
• Grounding of all parts, tools and the human body ( ESD workstation )
• Connect all external terminals of an IC, so that no potential difference can occur between these