Mechanism for vacuum thermal stabilization of silver in graphite-like carbon coating and performance of electrical conductivity and corrosion resistance

Abstract

To inhibit the spontaneous escape of silver from graphite-like carbon coatings, a series of silver-containing graphite-like carbon coatings were prepared by heated vacuum deposition. The effect of the substrate temperature during deposition on the spontaneous escape behavior of silver was studied, and a mechanism for vacuum thermal stabilization of silver is proposed. The results show that when the substrate temperature was increased from 80 to 250 °C, the thickness of the surface silver layer was reduced from 150 to 60 nm. When the substrate temperature was increased to 300 °C, no silver particles were found on the surface of the sample even after placing the sample in an atmospheric environment for 2000 h. Thus, heating in a vacuum can effectively suppress the spontaneous escape of silver and hence achieve the permanent retention of silver in the graphite-like carbon coatings. The electrical conductivity of the coating was close to that of a graphite plate, but the corrosion current density of this coating (7.147 × 10−6 A•cm−2) was an order of magnitude higher than that of the graphite plate. An approximately 300-nm silver-free carbon layer surface cover could effectively improve the corrosion resistance of the coating, and the conductivity of the coating satisfies the performance requirements for fuel cell plates. The growth of silver clusters that segregate at the interface of the graphite-like carbon clusters is promoted during coating deposition by the thermal activation energy of substrate heating, thereby inhibiting the spontaneous escape of silver caused by internal and external pressure differences.