Nanopore formation on the surface oxide of commercially pure titanium grade 4 using a pulsed anodization method in sulfuric acid

Abstract

Titanium and its alloys form a thin amorphous protective surface oxide when exposed to an oxygen environment. The properties of this oxide layer are thought to be responsible for titanium and its alloys biocompatibility, chemical inertness, and corrosion resistance. Surface oxide crystallinity and pore size are regarded to be two of the more important properties in establishing successful osseointegration. Anodization is an electrochemical method of surface modification used for colorization marking and improved bioactivity on orthopedic and dental titanium implants. Research on titanium anodization using sulphuric acid has been reported in the literature as being primarily conducted in molarity levels 3 M and less using either galvanostatic or potentiostatic methods. A wide range of pore diameters ranging from a few nanometers up to 10 μm have been shown to form in sulfuric acid electrolytes using the potentiostatic and galvanostatic methods. Nano sized pores have been shown to be beneficial for bone cell attachment and proliferation. The purpose of the present research was to investigate oxide crystallinity and pore formation during titanium anodization using a pulsed DC waveform in a series of sulfuric acid electrolytes ranging from 0.5 to 12 M. Anodizing titanium in increasing sulfuric acid molarities showed a trend of increasing transformations of the amorphous natural forming oxide to the crystalline phases of anatase and rutile. The pulsed DC waveform was shown to produce pores with a size range from ≤0.01 to 1 μm(2). The pore size distributions produced may be beneficial for bone cell attachment and proliferation.

Effect of duty cycle on the crystallinity, pore size, surface roughness and corrosion resistance of the anodized surface on titanium

“…In addition, the surface porosity of specimens anodized in each molarity was characterized as nano-sized surface roughness features. [46] The pulsed anodization waveform also produced smaller pore sizes and suggested higher anatase levels than those reported in previous potentiostatic and galvanostatic anodization studies. [16,47,48] The purpose of the present research was to investigate the effect of anodization waveform duty cycle on the formation of crystalline phases, surface transformations and corrosion resistance in Ringer's solution while maintaining a homogenous surface oxide color.…”

“…These findings also suggested that anodization in sulfuric acid results in formation of the anatase phase at approximately 70 V followed by the rutile phase at higher forming voltages, which is in good agreement with previous studies. [16,26,46] …”

“…The pre-anodization dip of specimens in a nitric acid-hydrofluoric acid solution has been reported in previous studies and is used to clean the specimen of any remaining residues. [46,[49][50][51] …”

“…with increased waveform duty cycle. [3,30,46] The formed oxide thickness is well documented to be related to the charge resulting from the applied forming voltage (potentiostatic) or current (galvanostatic) and to the interference color. [3,8,29,61].…”

“…[46] The results showed that the optimal sulfuric acid molarity for maximum anatase production for a dark green colored oxide was 2.8 M and 5.6 M for a gold colored oxide.. In addition, the surface porosity of specimens anodized in each molarity was characterized as nano-sized surface roughness features.…”