Sol-gel coating containing carbon quantum dots for effective corrosion prevention

Abstract

This study investigates the impact of carbon quantum dots (CQDs) on the corrosion protection properties of sol-gel coating on AM60B alloy. CQDs were synthesised via microwave technique and characterised using Field Emission Scanning Electron Microscopy (FESEM), Fourier Transform Infrared Spectroscopy (FTIR), X-ray Photoelectron Spectroscopy (XPS), and X-ray Diffraction (XRD). Adding 50 ppm CQDs eliminated micrometric cracks in the coating due to chemical bonding with the silica network. Transmission Electron Microscope (TEM) images revealed that CQDs are well dispersed at 50 ppm in the coating. Also, the Atomic Force Microscopy (AFM) confirmed that this concentration reduces the coating's roughness. Electrochemical Impedance Spectroscopy (EIS) in sodium chloride solution revealed a significant reduction in both electrical double- layer and sol-gel layer capacitances after adding 50 ppm CQDs. This indicates reduced penetration of the corrosive electrolyte, attributed to pore blocking and the elimination of micrometric cracks. After 48 h of immersion, the polarisation resistance (Rp) increased from 0.006 to 0.353 MΩ cm2, significantly enhancing the anti-corrosion performance. However, higher concentrations (100 and 200 ppm) of CQDs negatively impacted the corrosion resistance due to the accumulation and micrometric crack formation.