Method for reducing contact resistivity of carbon nanotube-containing epoxy adhesives for aerospace applications

Bonded joints prepared with conductive epoxy adhesive based on carbon nanotubes (CNTs) display an unusually high resistance mainly due to the high contact resistivity at the adhesive metal interface. A new method is proposed to reduce efficiently the contact resistivity by forcing a controlled amount of electric current through the bonded joint. Current treatment at 0.5 A/cm2 of current densities for 30 s typically reduces to up to 10 times the contact resistivity. Apart from noble metals, all other metals are usually covered by a more or less conductive oxide layer. This oxide layer is the main cause for high contact resistivity. During the current treatment large gradients of electric field developed around the highly curved CNTs are capable of breaking down locally the oxide layer generating conductive channels. Static shear strength and fatigue resistance of the bonded joint are not affected by the current treatment.