Morphology, Chemical Composition, and Electrochemical Characteristics of Colored Titanium Passive Layers

Abstract

Brightly and uniformly colored passive layers on Ti are formed by application of ac polarization in aqueous NH4BF4. A wide spectrum of well-defined colors is accomplished by varying the ac voltage. The passive films are stable in the ambient and in aqueous chloride, perchlorate, and sulfate solutions. Optical microscopy and scanning electron microscopy analyses indicate that the passive layers are compact and do not show fractures or cracks. An X-ray photoelectron spectroscopy (XPS) characterization of the colored passive layers demonstrates that their surface-chemical composition depends on the ac polarization voltage. The main constituents of the passive layers are Ti z+ , O 2-, and F -(z varies from 4 to 2 depending on the film's depth). Fluoride in the film originates from decomposition of NH4BF4, and it accumulates at the inner metal/passive-film interface. XPS depth profiling shows that the higher the ac voltage applied, the thicker the passive film formed. Electrochemical properties of the colored Ti passive layers are determined by recording polarization curves in the -0.8 to 3.2 V range as well as Tafel plots in the hydrogen evolution reaction (HER) region in 1.0 M aqueous H2SO4. The polarization curves show that the corrosion potential of the colored passive layers shifts toward less-negative potentials indicating that they are more stable than Ti under the same conditions. The passive region for the colored layers resembles that for Ti. The Tafel plots for the HER demonstrate that the passive layers have higher activity toward the HER than Ti. The Tafel relations reveal new features that can be associated with the partial breakdown/decomposition of the passive layers, H absorption, and the onset of Ti hydride formation.

Optical and Physical Properties of Cobalt Oxide Films Electrogenerated in Bicarbonate Aqueous Media

“…Such results confirm the transparent character of the films, as well as the occurrence of iridescence. This interference phenomenon, defined as constructive light interference between the beam reflected at the outer film-air interface and the inner metal-film interface, 63,64 induces the coloration of the films because their thicknesses, as determined by SE, AFM, and profilometry, are in the order of the wavelength of visible light. 65,66 It has already been mainly observed for titanium (e.g., refs 46, 63, 64, 67-70) and stainless steel (e.g., refs [71][72][73], but is here reported for the first time for cobalt.…”

Investigations on the self-organized growth of TiO2 nanotube arrays by anodic oxidization

“…Titanium oxide (TiO 2 ) nanotubes and nanostructure materials are of considerable interests for their applications in photovoltaic cell [1], photocatalysis [2], sensing [3,4], and biomedical industry [5,6] due to their unique physical and chemical properties [7][8][9]. Many approaches such as templating synthesis [10,11], hydrothermal reactions [5,12], and anodic oxidization [13][14][15][16][17] have been developed for preparing nanostructure materials.…”

Intraoperative Neuromonitoring

“…In fact, none of the 10 medially breached screws from this study would have been identified as such, based on screw stimulation alone [i.e., thresholds ranged between 11.8 and .30 mA, all exceeding the "accepted" upper cutoff of 6-11 mA reported by a number of previous studies (Calancie et al, 1994;Clements et al, 1996;Glassman et al, 1995;Kim et al, 2004;Lewis et al, 2001;Maguire et al, 1995;Raynor et al, 2003, Reidy et al, 2001Rodriguez-Olaverri et al, 2008;Samdani et al, 2010)]. Titanium, both alloyed and commercially pure, spontaneously forms a thin (,10 nm) native oxide when exposed to oxygen-containing media (e.g., air, blood) (Donley and Gillette, 1991;Hrapovic et al, 2001;Huang et al, 2003;Milosev et al, 2000;Scharnweber et al, 2002;Sul et al, 2001;Velten et al, 2002). Titanium, both alloyed and commercially pure, spontaneously forms a thin (,10 nm) native oxide when exposed to oxygen-containing media (e.g., air, blood) (Donley and Gillette, 1991;Hrapovic et al, 2001;Huang et al, 2003;Milosev et al, 2000;Scharnweber et al, 2002;Sul et al, 2001;Velten et al, 2002).…”

“…Titanium, both alloyed and commercially pure, spontaneously forms a thin (,10 nm) native oxide when exposed to oxygen-containing media (e.g., air, blood) (Donley and Gillette, 1991;Hrapovic et al, 2001;Huang et al, 2003;Milosev et al, 2000;Scharnweber et al, 2002;Sul et al, 2001;Velten et al, 2002). These increases in oxide thickness, or crystallinity, correlated with transitions in the apparent color of the implant (Hrapovic et al, 2001;Sul et al, 2001;Velten et al, 2002). These anodization treatments cause the natural oxide to thicken, gradually organizing into a crystalline structure that can become highly porous (Aladjem, 1973;Kim and Ramaswamy, 2009;Park et al, 2007;Zhu et al, 2001).…”

“…Additionally, the surfaces of these screws are typically subjected to electrochemical anodization treatments to generate specific colors of the surface oxides to allow for easy identification of the type of screw (e.g., length, diameter, fixed or variable head). As the oxide becomes thicker or more crystalline, a set spectrum of visible colors (i.e., wavelengths of light being reflected and absorbed) is established (Hrapovic et al, 2001;Sul et al, 2001;Velten et al, 2002). These increases in oxide thickness, or crystallinity, correlated with transitions in the apparent color of the implant (Hrapovic et al, 2001;Sul et al, 2001;Velten et al, 2002).…”