| Uniform and crack-free colored passive films on commercially pure (CP) titanium implant, TMA and TiNb orthodontic wires are prepared using AC (alternating current) electrochemical passivation in aq. NH4BF 4. The passive films reveal a wide spectrum of colors, which are originated from iridescence. The surface morphology, chemical composition, thickness, wettability, corrosion behavior and metallic ion release in simulated body fluids (SBFs) at 37°C of these passive films are characterized using surface-science tools, analytical techniques, and electrochemical measurements.; Surface profilometry, optical microscopy, scanning electron microscopy (SEM) analyses, and contact angle measurements show that the passive films on CP titanium are uniform, make the surface rougher and more hydrophilic. Electrochemical measurements demonstrate that the AC passivation makes titanium more stable, reduces its corrosion rate (CR) and titanium ion release level in Hank's Balanced Salt Solution (HBSS).; In the case of TMA and TiNb, the passive films make their surface slightly rougher, more stable and more corrosion resistant, and reduce the metallic ion release in artificial saliva. Nitric acid chemical passivation of the chemically etched TMA does not improve its corrosion resistance. Auger Electron Spectroscopy (AES) depth profiles show that the passive films formed on TMA are primarily composed of TiO2 in the outer layer and a mixture of TiO2 and MoO3 in the inner layer, plus a small amount of fluoride that originates from NH4BF4 decomposition during the passivation. There is a linear rise of the passive film thickness with the increase of VAC.; The surface morphology of the passive films formed on CP titanium, TMA and TiNb using AC passivation reveals the memory effect from the corresponding substrates.; The AC passivation of NiTi does not enhance its corrosion resistance, and micro cracks are observed on the surface. Chemical etching followed by chemical passivation or aging in boiling water shows an enhanced corrosion behavior in artificial saliva.; The AC passivation is an effective way to prepare biocompatible passive films and might find applications as a new surface treatment procedure for CP titanium implants, TMA and TiNb orthodontic wires. Chemical etching followed by aging is recommended for surface treatment of NiTi orthodontic wires. |
