Effect of morphology on the electrophoretic deposition of hydroxyapatite nanoparticles

Highlights: • FHA particles aligned mostly horizontally and randomly at low and high voltages, respectively. • FHA coatings are reinforced by interlocked particles and have less drying shrinkages. • Parallel cracks are generated in FHA coatings deposited from methanol at low voltages. • Parallel cracks are diminished in FHA coatings deposited at higher voltages. • SHA coating effectively decreased the corrosion rate of substrate due to its less pores. Electrophoretic deposition (EPD) was performed from alcoholic suspensions of spherical (SHA) and fiber (FHA) hydroxyapatite nanoparticles. FHA particles were horizontally aligned in deposits prepared at lower voltages since they can find enough space and time to rotate upon reaching the deposit and sit horizontally on it. While, they are more randomly oriented at higher voltages since more FHA particles aligned parallel to electric field reach to the substrate and also particles cannot find enough time and space for rotation. FHA particles are highly interlocked together in FHA deposits reinforcing them and also the drying shrinkages are lower for them resulting in their less cracking. The cracks are parallel to each other in FHA coating deposited from methanolic suspension at 5 V due to the more horizontal and parallel alignment of FHA particles in it. The crack-free SHA coating decreased the corrosion rate of substrate more efficiently due to its less porosity.