Hygrothermal Stability of Electrical Contacts Made from Silver and Graphite Electrically Conductive Pastes

Abstract

The hygrothermal stability of electrical contacts made from silver and graphite electrically conductive pastes is comparatively evaluated by measurement of the increase in contact electrical resistance during immersion in water at 15°C and 40°C. The pastes are silver paint, silver paint with a nonconductive epoxy overcoat, silver epoxy, and graphite colloid. Each electrical contact is made between a seven-strand tin-coated copper wire and the surface of a carbon fiber epoxy-matrix composite. Silver paint and graphite colloid penetrate the spaces among the 130-lm-diameter strands, but silver epoxy does not. Partly due to its low penetrability and the silver flake (15 lm) preferred orientation, silver epoxy gives contacts of significantly higher resistance than silver paint. Graphite colloid is comparable to silver epoxy in the resistance. Among the four pastes, silver paint with an epoxy overcoat is most durable, though it gives slightly higher resistance than silver paint without epoxy. Silver epoxy is less durable than silver paint without an epoxy overcoat, particularly at 40°C, due to the low hygrothermal stability of epoxy. Graphite colloid is even less durable than silver epoxy, due to its being water based.

Electrical-resistance-based Sensing of Impact Damage in Carbon Fiber Reinforced Cement-based Materials

“…Silver paint is a suspension of silver particles in a volatile solvent (Leong and Chung, 2006;Wang et al, 2007). Upon evaporation of the solvent, the silver particles touch one another, thereby providing high electrical conductivity.…”

Damage detection using self-sensing concepts

“…The wire must be in electrical contact with all the laminae, so it should be electrically connected to the wall of the through-hole by using a conductive adhesive or other conductive media. Silver particle filled epoxy is a conductive adhesive that has been shown to perform well both electrically and mechanically [26,27]. However, this type of electrical contact suffers from its intrusiveness, as the drilling of a hole may cause some local damage to the composite.…”

“…An additional problem with the two-probe method relates to the possible degradation of the electrical contacts upon strain or damage of the specimen under test. The degradation of the contacts causes the contact resistance to increase, thus affecting the resistance that is obtained by using the two-probe method [25,26]. In the case of the four-probe method, degradation of the contacts has relatively little effect on the measured resistance, unless the degradation is excessive.…”

“…The conductive medium serves to connect electrically the composite surface to a lead wire that goes to a meter. In order to enhance the mechanical integrity and hygrothermal stability of the surface electrical contacts, each contact (such as one made by using silver paint) may be coated with non-conductive epoxy [26].…”

Improving the Crystallinity and Purity of Monodisperse Ag Fine Particles by Heating Colloidal Sprays In-Flight

“…Compared with this standard process, the method proposed in this paper is much more rapid (requiring only several seconds) and, as a result, sintering of the particles and concurrent significant size increases are avoided. Ag particles were selected as a test material because Ag has many applications, such as in conductors, electrical contacts, catalysts, and wound dressing. − In particular, correlations between the heating temperature and particle characteristics (including crystallinity, morphology, size, distribution, purity, and volume resistivity) were investigated in detail. A possible mechanism for producing isolated fine metal particles is suggested based on the experimental results and available theory.…”