The Triboelectric effect reference article from the English Wikipedia on 24-Jul-2004 (provided by Fixed Reference: snapshots of Wikipedia from wikipedia.org)

Triboelectric effect

The triboelectric effect is an electrical phenomenon where certain materials, for example, glass, hard rubber, amber, or clothing, become electrically charged after coming into contact with another, different, material.

For example, glass rubbed with silk will build up a charge, as will hard rubber rubbed with fur. The polarity and strength of the charges produced differ according to material and surface smoothness.

Although the word comes from the Greek for "rubbing", tribos, the two materials only need to come into contact and then separate for electrons to be exchanged. After coming into contact, a chemical bond is formed between some parts of the two surfaces, called adhesion. When separated, some of the bonded atoms have a tendency to keep extra electrons, and some a tendency to give them away. This is what creates the net charge imbalance between the objects. The triboelectric effect is only related to friction because they both involve adhesion. However, the effect is greatly enhanced by rubbing the materials together, as they touch and separate many times.

Materials are often listed in order of the charge built up when they are touched with another object. This is called the triboelectric series:

• Dry human skin (Most positively charged)
• Asbestos
• Leather
• Rabbit's fur
• Glass
• Mica
• Human hair
• Nylon
• Wool
• Lead
• Cat's fur
• Silk
• Aluminum
• Paper (Small positive charge)
• Cotton (No charge)
• Steel (No charge)
• Wood (Small negative charge)
• Lucite
• Amber
• Sealing wax
• Acrylic
• Polystyrene
• Rubber balloon
• Resins
• Hard rubber
• Nickel, Copper
• Sulfur
• Brass, Silver
• Gold, Platinum
• Acetate, Rayon
• Synthetic rubber
• Polyester
• Styrene (Styrofoam)
• Orlon
• Saran wrap
• Polyurethane
• Polyethylene (like Scotch tape)
• Polypropylene
• Vinyl (PVC)
• Silicon
• Teflon
• Silicone rubber (Most negative charge)

A material towards the bottom of the series, when touched to a material near the top of the series, will attain a more negative charge, and vice versa. The further away two materials are from each other on the series, the greater the charge transferred. Materials near to each other on the series may not exchange any charge, or may exchange the opposite of what is implied by the list. This depends more on other properties than the type of material. Lists vary somewhat as to the exact order of some materials, since the charge also varies for nearby materials.

Because the material is now electrically charged, either negatively or positively, contact with an uncharged object or one with a substantially different charge may cause a discharge of the built-up static electricity; a spark. A person simply walking across a carpet may build up a charge of many thousands of volts, enough to cause a spark a centimeter long or more (this type of discharge is usually harmless, as it passes very little current).

The effect is of considerable industrial importance both in terms of safety and also potential damage to manufactured goods. The spark produced is fully capable of igniting inflammable vapours, for example, petrol or ether fumes. Means have to be found to discharge hospital trolleys which may carry such liquids.

Even where only a small charge is produced, this can result in dust particles being attracted to the rubbed surface. In the case of textile manufacture this can lead to a permanent grimy mark where the cloth has been charged.

This effect is the principle behind the charge build-up in a triboelectric-type Van de Graaff generator.

External links

• http://www.cleanairsystems.com/__data/page/1560/Triboelectrics.pdf