Surface Tension

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Definition - What does Surface Tension mean?

Surface tension is the force that causes the molecules on the surface of a liquid to be pushed together and form a layer. It is the tension of the surface film of a liquid caused by the attraction of the particles in the surface layer by the bulk of the liquid, which tends to minimize surface area.

Surface tension has the dimension of force per unit length, or of energy per unit area. It is typically measured in dynes/cm, the force in dynes required to break a film of length 1 cm.

Corrosionpedia explains Surface Tension

Surface tension is a property of a liquid surface that causes it to act like a stretched elastic membrane. Its strength depends on the forces of attraction among the particles of the liquid itself and with the particles of the gas, solid or liquid with which it comes in contact. Surface tension is equal to the amount of force per unit area necessary to expand the surface of a liquid. The cohesive forces between liquid molecules are responsible for the phenomenon known as surface tension.

Due to relatively high attraction of water molecules for each other, water has a high surface tension compared to that of most other liquids. Because of this, certain insects are able to stand on the surface of water, and a razor blade placed horizontally on the liquid's surface can be supported, even though the blade may be denser than the liquid and unable to float.

The surface tension of water decreases significantly with temperature. Surfactants (soaps and detergents) are also used to lower the surface tension of water. Surfactants are important corrosion inhibitors that are used in applications like cooling towers and heat exchangers to reduce surface tension.

Surface tension can cause pitting. For example, a typical chrome bath has a surface tension between 75 and 90 dynes/cm. This high surface tension has been linked to pitting in some cases. The surface tension of a solution should be maintained within the recommended range of 28 - 34 dynes/cm. This range prevents pitting that can result from hydrogen generated at the cathode clinging to the deposit. The concentration of wetting agent in the bath is determined through measurement of the surface tension with the use of a stalagometer drop test.

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