Properties Enhancement of an Eco-Friendly Electrical Contact Material by Silver Nanoparticles Addition
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ilver-cadmium oxide has long been the contact material of choice for a wide range of low-voltage applications from 15 to 5000 A due to its excellent antiwelding and long life characteristics. Very favorable thermodynamic characteristics of cadmium oxide proved an excellent behavior and a wear mechanism in electrical arc that was unseen in other contact materials.[1–3] Silver-tin oxide materials are gradually replacing silver-cadmium oxide ones due to ecological issues and environmental regulations concerning the use of toxic cadmium oxide in electrical contacts since it is emitted into the environment as the contact elements burn off.[4–7] Silver-tin oxide contact elements burn off less than do silver-cadmium oxide ones, thereby resulting in longer life, but they develop a higher transfer resistance than silver-cadmium oxide since an oxide layer forms due to its higher thermal stability and arcing effects. In the current-carrying state of the switchgear, the oxide layer leads to overtemperatures that can damage the switchgear.
MAGDALENA LUNGU, STEFANIA GAVRILIU, MARIANA LUCACI, VIOLETA TSAKIRIS, and GIMI RIMBU, Senior Researchers, and ELENA ENESCU, Senior Researcher and Deputy Director, are with the National Institute for Research and Development in Electrical Engineering ICPE-CA, 030138 Bucharest 3, Romania. Contact e-mail: [email protected] Manuscript submitted May 25, 2012. METALLURGICAL AND MATERIALS TRANSACTIONS A
Usually, basic compositions of silver-tin oxide materials contain 6 to 14 wt pct stannic oxide and up to 2 wt pct additions of tungsten trioxide, molybdenum trioxide, bismuth trioxide, copper oxide, ferrous tungstate, or other compounds to reduce the buildup of nonconductive oxide layers on the contact surface and to tailor the properties to match the specific requirements.[4–10] Nanopowders in particular and submicron powders in general represent a new family of material precursors where conventional coarse-grain physiochemical mechanisms are not applicable. These materials, especially noble metal nanoparticles whose small size confinement effects become a significant determinant of the performance of the materials, offer unique combination of properties.[11–16] In this study, a silver-tin oxide material with 10 wt pct stannic oxide and balance nanosized and microsized silver with tailored and improved properties due to an ideal microstructure model is investigated. It consists in fine spherical particles of stannic oxide chemically coated by a layer of silver nanospheres in 28 wt pct and uniformly dispersed in a silver microcrystalline matrix made by chemical synthesis in situ. The raw materials used in synthesis were of analytical grade without further purification (Merck or SigmaAldrich, Darmstadt, Germany). The deposition of spherical silver nanoparticles with average diameter of 40 nm on stannic oxide particles with average diameter of 1000 nm was carried out by chemical synthesis in situ by reduction of silver cations from a 5-mM silver nitrate solution containing stannic oxide particles, in tw
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