Difference between revisions of "Triboelectricity"

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Though the discharge energy from this spark is typically small (tens of microjoules for a typical person-doorknob spark), it can be very dangerous near combustibles.  Items can be made resistant to the triboelectric effect by giving them a conductive coating; typical anti-static materials include long-chain aliphatic amines and amides, ammonium salts, esters of phosphoric acid, polyethylene glycol esters, polyols, conductive polymers, and Indium Tin Oxide.
 
Though the discharge energy from this spark is typically small (tens of microjoules for a typical person-doorknob spark), it can be very dangerous near combustibles.  Items can be made resistant to the triboelectric effect by giving them a conductive coating; typical anti-static materials include long-chain aliphatic amines and amides, ammonium salts, esters of phosphoric acid, polyethylene glycol esters, polyols, conductive polymers, and Indium Tin Oxide.
 
 
  
 
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Revision as of 23:33, 16 November 2008

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Introduction

Story about the Greeks or other ancients and what they knew about triboelectricity?

From the wikipedia:

"The triboelectric effect (also known as 'triboelectric charging') is a type of contact electrification in which certain materials become electrically charged after they come into contact with another different material and are then separated (such as through rubbing). The polarity and strength of the charges produced differ according to the materials, surface roughness, temperature, strain, and other properties."

The first to organize a series was Volta in 1779. Modern lists give:

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

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Physical Origin

The basic cause for the triboelectric effect is the formation of bonds between contacting surfaces that result in charge imbalance when the bond is broken by removing the objects from contact. When two objects contact, a chemical bond can be formed between some parts of the two surfaces (adhesion). In some cases, charges may move from one item to the other to minimize electrochemical potential, creating a net charge imbalance. When the objects are then separated, the bonds can be broken in a way such that the net charge imbalance remains. Though the triboelectric effect is usually associated with rubbing, the rubbing itself does not play a crucial role; it merely allows for many contact cycles thus resulting in a larger charge buildup.

Now that the object is electrically charged, contact with a neutral conductor (or any object having significantly differing electric charge) may result in a discharge of the built-up static. A person walking across a carpet may build up a charge of up to several thousand volts, enough to cause a spark in air (which has a dielectric breakdown of ~30,000 V/cm).

Though the discharge energy from this spark is typically small (tens of microjoules for a typical person-doorknob spark), it can be very dangerous near combustibles. Items can be made resistant to the triboelectric effect by giving them a conductive coating; typical anti-static materials include long-chain aliphatic amines and amides, ammonium salts, esters of phosphoric acid, polyethylene glycol esters, polyols, conductive polymers, and Indium Tin Oxide.

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Luigi Galvani

In 1783, according to popular version of the story, Galvani dissected a frog at a table where he had been conducting experiments with static electricity, Galvani's assistant touched an exposed sciatic nerve of the frog with a metal scalpel, which had picked up a charge. At that moment, they saw sparks and the dead frog's leg kick as if in life. The observation made Galvani the first investigator to appreciate the relationship between electricity and animation — or life




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