How Is Static Created ?

There are three main causes of static electricity; friction, separation and induction.

Friction

As two materials are rubbed together the electrons associated with the surface atoms on each material come into very close proximity with each other. These surface electrons can be moved from one material to another. The direction in which the electrons travel either from Material A to Material B or vice versa depends on the Triboelectric Series. Materials on the positive side of the Triboelectric Series will tend to give up their surface electrons and become positively charged whilst conversely materials on the negative side of the series tend to gain electrons and hence a negative charge. The harder the two materials are pressed together the greater the exchange of electrons and hence a higher charge is generated. A practical example is if a piece of polythene is rubbed on a nylon carpet with gentle force a moderate negative charge will be generated on the polythene, whereas if the force is increased a larger negative charge will be achieved. The speed of the rubbing action also has that effect on the level of charge, the faster the rubbing the higher the level of charge. This is due to the surface electrons gaining heat energy generated by the friction. This extra energy allows them to break their atomic bonds and transfer to other atoms.
Separation
The method of charging by separation is similar to that of friction. When two materials are in contact the surface electrons are in close proximity to each other and upon separation have a tendency to adhere to one material or the other dependent upon their relative positions on the Triboelectric Series. The faster the separation of the materials, the higher charge generated and conversely, the slower the separation the lower the charge. A common example is of a PVC web moving over a Teflon coated roller, as the materials separate the electrons will tend to adhere to the Teflon, generating a net negative charge on the Teflon and a net positive charge on the PVC.
Induction
Whilst of interest technically, induction does not play a significant role in our field. Static charges can be generated when materials are in the presence of a strong electric field.
The surface of a material in close proximity to a high positive voltage will tend to become positively charged. The method of charging is caused by ionisation of the air between the surface of the material and the voltage source which carries surface electrons away from the material to the source, (ionisation is explained in methods of elimination). An example of induction is operators working near charged materials. The operator will himself become charged and on touching an earthed object will discharge to it, giving the operator an electric shock – often mistaken for a shock from the mains supply.

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