TEM and zeta potential titration as suitable techniques for investigating the joining of modified ceramic surfaces

Transmission Electron Microscopy (TEM-EDS) and Zeta potential titration of ceramic surfaces allowed researchers to go inside their adhesion mechanism when joined with an adhesive. The case study concerned the plasma Corona treatment to improve the joint strength between SiC surfaces joined with an epoxy adhesive. The formidable mechanical and chemical properties inherent to silicon carbide pose challenges in applying conventional methods like mechanical machining and wet etching for surface texturing. Exploring alternative strategies, plasma Corona treatment which is an Atmospheric Pressure Plasmas (APPs) process emerges as a potential solution. The mechanism of chemical interaction and mechanical interlocking between plasma-treated surfaces and the epoxy adhesive used for the joining was never explored in detail and proven. The presence of layers with different crystallographic natures and chemical compositions was assessed by TEM-EDS: an amorphous silica layer was produced by the corona activation treatment and it created a mechanical anchoring system when penetrated by the adhesive. The zeta potential titration as a function of pH evidenced that untreated SiC had a surface with amphoteric functional groups, while the Corona treatment induced the formation of surface functional groups (OH) with a strong acidic behavior on SiC. The investigated epoxy adhesive exposed a prevalence of basic amino groups. Zeta potential titration curves highlighted the chemical interaction between the treated SiC surfaces and the epoxy adhesive: the large electrostatic attraction between the OH groups of the treated SiC and the amino groups of the epoxy adhesive had a role in the mechanical strength of the joining. TEM and Zeta potential titration can be proposed as suitable techniques to evaluate the effectiveness of the plasma corona discharge system in modifying the surface of SiC and to solidify its standing in comparison to other established surface modification techniques to improve SiC-based joints.