We investigated the anodic dissolution of polycrystalline titanium rotating disc electrode in 0.1 M hydrofluoric acid in active and passive regions using potentiodynamic polarization and electrochemical impedance spectroscopy. In the active region, complex plane plots of the impedance spectra exhibited three capacitive loops indicting the presence of at least two adsorbed intermediates. In the passive region, they exhibited a negative resistance and a low frequency inductive loop. The high frequency loops exhibit constant phase element behavior indicating that a heterogeneous 2D film with partial surface coverage is present in the active and passive regions. The impedance data was fit to a reaction model and a four step mechanism with two adsorbed intermediate species is proposed to explain the observed trends in the active and passive regions. The change in the surface coverage of the adsorbed intermediate species, with the overpotential is estimated. This model describes the dissolution of Ti via two parallel paths, viz. a chemical step and an electrochemical step. The onset of passivation ensues when the rate of TiO 2 film formation is more than that of its dissolution. Transpassive dissolution becomes dominant when the electrochemical dissolution from the bare surface becomes negligible. Titanium metal and its alloys are widely used in engineering applications and medical implants, due to their low density, high corrosion resistance and high strength.1 These materials possess excellent corrosion resistance in acidic media, through the formation of protective oxide film on the metal surface. In order to facilitate the attack of the passive oxide layer, solutions containing fluoride ions are used for the anodic dissolution of titanium. [2][3][4] The corrosion studies of titanium show that at low overpotentials, the dissolution is in active region, and at moderate overpotentials, surface passivation occurs. At high overpotentials, transpassive dissolution is observed.The dissolution mechanism of titanium in solutions, with and without fluoride ions have been characterized using various techniques. The dissolution of Ti in 10 M H 2 SO 4 was investigated using polarization and impedance techniques 5 and it was reported that the dissolved species is Ti 3+ . To the best of our knowledge, the earliest report on electrochemical studies of Ti dissolving in acidic fluoride ions was published by Kelly.6 Polarization studies show clear active, passive and transpassive regions. 6 The impedance spectrum was acquired in the transpassive region and was analyzed to show that the film thickness increased with the potential. 6 The impedance of Ti in solutions containing strong acids (H 2 SO 4 and HNO 3 ) along with 0.1 mM -10 mM hydrofluoric acid was analyzed 4 and a four step reaction mechanism involving Ti + , Ti 2+ and Ti 3+ adsorbed intermediate species and Ti 3+ dissolved species was proposed to explain the results. In each case, the spectra were acquired at only one potential. The confidence in the model identification wo...

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Particles with size in the range of 1-100 nm, considered in any dimension, are called nanoparticles (NPs). Among various nanoparticles, nickel oxide nanoparticles (NNPs) are important because of their physical, chemical, and biological properties. In the past two decades, significant research has been done on the synthesis of NNPs. Their applications range from energy storage to catalysis to antifungal and antibacterial activity. This review provides a brief overview of various methods used for synthesizing NNPs, their properties, and their applications. The synthesis methods are classified into physical synthesis, chemical synthesis, and green synthesis involving plants and microorganisms, especially fungi. Particular focus is given to the types of precursors used for their synthesis, morphology, particle size, and applications.

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