Electrophoretic deposition of hydroxyapatite nanoparticles in different alcohols: Effect of Tris (tris(hydroxymethyl)aminomethane) as a dispersant

The suspensions of HA nanoparticles (20 g/L) in different alcohols (methanol, ethanol, isopropanol and butanol) were prepared and Tris (tris(hydroxymethyl)aminomethane) was used as a dispersant to enhance their colloidal stability. It was found that H+Tris ions generated through the Tris protonation in the alcoholic suspensions are chemically adsorbed on the HA nanoparticles via hydrogen bonding with their surface P–OH groups increasing their zeta potential and so their colloidal stability. It was found that the higher the molecular weight of alcohol the lower the concentration of generated H+Tris ions in them; so the higher concentration of Tris should be added into them to saturate the surface of HA nanoparticles with H+Tris ions leading to the higher amounts for optimum concentration of Tris in them. Electrophoretic deposition (EPD) was performed at 60 V for different times. EPD kinetics was the fastest from the suspensions with optimum concentration of Tris due to the highest zeta potential and so the highest mobility of particles in them. The coatings deposited from the suspensions with optimum concentration of Tris had the uniform, fine and agglomerate-free microstructure; so these coatings can act as the effective barrier against the corrosive fluid to reach the substrate surface leading to the higher reduction in corrosion rate of substrate.