Nature of the adhesion bond between epoxy adhesive and titanium

The time dependence of the potential difference that appears between two VT6 titanium alloy plates separated by a mixture of epoxy resin with an epoxy hardener is studied. One of the plates is placed in epoxy resin until equilibrium is established, and the second plate is coated with an as-prepared mixture of epoxy resin and a hardener. It is found that the potential difference decreases in time because of charge transfer by Ti$^{2+}$ ions through epoxy resin. Photoluminescence and infrared absorption spectra of epoxy adhesive on the VT6 alloy surface are recorded. Their analysis shows that the Ti$^{2+}$ ions having penetrated into the as-prepared mixture of epoxy resin and a hardener interact with CN groups in adhesive molecules to form coordination compounds. As a result, a diffusion layer saturated with coordination compounds forms at the alloy/adhesive interface, which leads to an increase in the strength of the adhesive.