AgI as a solid lubricant in electrical contacts

• AgI coatings have been deposited by electroplating on Ag plated Cu coupons. Electron microscopy shows that the coatings consist of weakly agglomerated AgI grains. X-ray diffraction, differential scanning  calorimetry, thermogravimetry and mass spectrometry show that the AgI exhibits a reversible transformation from hexagonal to cubic phase at 150 °C. AgI starts to decompose at 150 °C with an accelerating rate up to the AgI melting temperature (555 °C), where a complex-bonded  hydroxide evaporates. Ag-pin-on-disk testing shows that the iodine addition to Ag decreases the friction coefficient from 1.2 to ~0.4. The contact resistance between AgI and Ag becomes less than 100 μΩ after ~500 operations as the AgI deagglomerates and Ag is exposed on the surface, and remains low during at least 10000 reciprocating operations. This makes AgI suitable as a solid lubricant in electrical contacts.

Nyckelord

Silver Iodide; Friction coefficient; Contact resistance; TEM; Phase transformation; DSC

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