The effect of various silver tin oxide materials on contact performance under motor load (a.c.)
The new contact material AgSnO/sub 2/ which is replacing AgCdO in many applications, requires the addition of additives to improve electrical contact performance. These additives such as copper oxide (Cu/sub 2/O) and bismuth oxide (Bi/sub 2/O/sub 3/), can significantly affect contact performance. An investigation was undertaken to compare the changes in contact performance between silver cadmium oxide (internally oxidized) and three silver tin oxide based materials containing (1) no additive, (2) copper additive and (3) bismuth plus copper additives. Performance changes and physical characteristics of each material such as formability (tensile properties), contact resistance and contact material erosion (arc erosion) were evaluated. The silver tin oxide based materials containing copper additive exhibited significantly higher resistance to arc erosion than silver cadmium oxide based material and other silver tin oxide materials evaluated. The resistance to welding and changes in electrical resistance were dependent on the chemistry of each material. The results suggested that the chemistry of the material was the chief reason silver tin oxide based material with copper additive performed better than silver cadmium oxide based material under identical motor load.
Metallurgical aspects of silver-based contact materials for air-break switching devices for power engineering
The properties of the contact materials Ag/CdO, Ag/SnO/sub 2/, Ag/Ni, Ag/C, and Ag/W are discussed on the basis of the metallurgical processes occurring due to the interaction of an electric arc with the contact material. In the case of Ag/CdO and Ag/SnO/sub 2/, the arc erosion behavior is characterized by the interplay between decomposition of the oxide component (energy consumption) and viscosity effects due to the oxide particles in suspension in the silver melt. With Ag/Ni the process of dissolution and reprecipitation of the Ni appears to be the dominant factor. The switching behavior of Ag/C is largely governed by the combustion reaction between the graphite particles and the oxygen of the atmosphere. The erosion resistance of Ag/W and Ag/WC, respectively, is mainly brought about by the high melting point of the W or WC component. By means of selected examples taken from the authors' research work and field experience, it is pointed out how the contact properties are influenced by the metallurgical mechanisms involved. It is shown that every material with a special advantage in one particular property also has a pronounced disadvantage in some other properties. >
Measuring Sheet Resistances of Dielectrics Using Co‐Planar Hydrogel Electrochemical Cells with Practical Applications to Characterize the Protective Quality of Paints on Sculptures
Electrical properties of thin dielectric films at the solid-liquid phase boundary are an important performance characteristic of many devices, coatings and sensors. In this paper, co-polymeric hydrogels of polyacrylic acid co-sulfonic acid, swollen with a salt solution to act as the solid electrolyte, were used to assess interfaces using electrochemical impedance spectroscopy (EIS) in a co-planar geometry. Silane-modified glasses were characterized by the co-planar hydrogel EIS cell and found to be distinguishable based on their surface monolayer chemistry. EIS measurements were also made on primed and painted metal substrates, using both test panels and an outdoor sculpture, Tony Smith's Stinger. The panels were then exposed to accelerated and outdoor weathering and showed degradation on the surface paint layers, which was observable electrochemically using EIS and confirmed visually by SEM. Electrochemical spectral features were compared between data from a standard paint-test cell versus this co-planar hydrogel cell; both cell types were able to measure coating capacitance, providing useful information about the condition of the bulk coating. Yet, sheet resistance (Rs) was a spectral feature seen only by the co-planar hydrogel cell. Thus, it can be concluded that the use of such co-planar hydrogel cells can provide an earlier warning sign to coating degradation and such cells provide a new type of spectral information that is not assessable by the standard geometry.