Electrodeposited zinc cellulose nanocrystals composite coatings: Morphology, structure, corrosion resistance and electrodeposition process

Nanoparticles, particularly ceramic, have been widely investigated as beneficial additives in electrodeposited zinc coatings. However, exploiting cellulose-based nanocrystals derived from plant sources is attractive due to their cost-effectiveness and sustainability. In this work, we assessed the impact of various concentrations of cellulose nanocrystals, ranging from 0 to 8 v/v%, on the characteristics of zinc coatings obtained through electrodeposition. We investigated the morphology and structure of the zinc deposits using scanning electron microscopy (SEM), x-ray diffraction (XRD), and confocal microscopy (CM). Corrosion resistance was evaluated through mass loss measurements and electrochemical tests including DC (potentiodynamic polarization) and AC (electrochemical impedance spectroscopy) measurements. Increasing cellulose nanocrystal concentrations up to 7 v/v% notably enhanced the corrosion resistance in 0.5 M NaCl solution. In comparison to coatings with no cellulose addition, the 7 v/v% cellulose concentration resulted in: i) an increase in polarization resistance from 586 Omega cm(2) to 1850 Omega cm(2), ii) a decrease in corrosion current density from 3.21 x 10(-5) A/cm(2) to 0.76 x 10(-5) A/cm(2), and iii) a reduction of the corrosion rate from 0.15 mm/year to 0.08 mm/year assessed after 24-h immersion. Furthermore, the addition of this optimal concentration of nanocrystals enhanced current efficiency to approximately 95%, without compromising microhardness, which remained around 184 HV0.1. Additionally, the incorporation of cellulose nanocrystals resulted in a more compact coating with reduced roughness (Ra similar to 0.69 mu m). This work thus showcases the significant and beneficial impact of cellulose nanocrystals in producing enhanced electrodeposited zinc coatings.