Electrodeposited hydroxyapatite coatings on the TiO2 nanotube in static magnetic field

Uniform hydroxyapatite (HA) grains were electrochemically deposited on the titania nanotube arrays (TNTs) in an electrolyte containing 0.042 mol/L calcium nitrate (Ca(NO3)2) and 0.025 mol/L ammonium dihydrogen phosphate (NH4H2PO4) in static magnetic field and then characterized by SEM, XRD, EDS, FTIR. To study the effect of magnetic fields on the morphology and adhesive strength of HA coatings on TNTs, the specimens were deposited in magnetic fields of different directions and intensities. The results indicate that the morphologies of HA crystals are plate-like, needle-like and spherical when the specimens were deposited in force-free magnetic field (B = 0), in the magnetic field perpendicular (B ⊥ J) and parallel to the current direction (B ∥ J), respectively. Due to the action of the Lorentz force, which generates convection in the electrolyte, mass transport may increase significantly. This main effect in electrochemistry was called the magnetohydrodynamic (MHD) effect and is well-established. Additionally, increasing the intensity of magnetic fields improves the adhesive strength of HA coatings: as the intensity increases from 0.25 T to 1 T, the adhesive strengths of composite electrodeposited in perpendicular and parallel conditions, respectively, increase from 20.1 MPa and 16.7 MPa to approximately 26.5 MPa and 24.7 MPa that are almost 2.5 times as strong as the control specimen.