Tailoring the Surface Functionalities of Titania …
529
8 Anodization of Titanium Alloys
Basically, titanium alloys are classified as α, near-α, α + β, metastable β, or stable β
depending upon the room temperature microstructure [87]. In this aspect, titanium
alloying elements can be classified as α-stabilizers (Al, O, N, C), β-stabilizers (Nb, V,
Ta, Fe Cr, Si, Co, Mn) and neutral such as Zr [72]. Titanium alloys are widely used in
hard tissue replacements in artificial bones, joints and dental prosthetic applications.
Various attractive properties of the Ti-based alloys such as high corrosion resistance,
exceptional mechanical properties and good biocompatibility were the driving force
for the early introduction of α (Cp-Ti) and α + β (Ti–6Al–4 V, Ti-6Al-7Nb) alloys
as well as the more recent development of modern and orthopaedic metastable β
Ti and β stabilized Ti alloys [16, 27]. Several studies reported the formation of
nanotubes on different Ti alloys [61, 88–94]. Nakada et al. [95] suggested using TiNb-Ta-Zr (TNTZ) alloy for orthopaedic implants because of its exceptional mechanical properties, biocompatibility and anticorrosion properties. In another study, an
anodized nanotube oxide layer with two size scale structures was reported on Ti28Zr-8Nb alloy using buffered electrolyte [96]. The influence of alloy composition
on the formed anodic oxide layer morphology on binary titanium alloys such as
Ti-xTa, Ti-yZr, and Ti–Al was investigated by the researchers [89, 97]. The study
revealed the formation of nanotube arrays on Ti-Zr alloy with a decreased diameter and increased tube length with increasing zirconium content. A tantalum oxide
(Ta 2 O 5 ) porous layer with pore diameter ranges from 2 to 35 nm on tantalum metal
can be formed electrochemically in acid-containing HF as electrolyte [98]. Highly
ordered Ta 2 O 5 nanoporous layer have grown on tantalum foils by anodization using
glycerol and NH 4 F containing electrolyte and it was found that average pore diameter
and thickness were affected by the NH 4 H concentration [99].
Anodization of CP Ti and titanium alloys (Ti-6Al-4 V, Ti-6Al-7Nb, Ti-13Nb13Zr, and β-21s) has investigated at optimized parameter [61]. FESEM images (left
side at lower and right side at higher magnifications) of anodic TiO 2 nanotube arrays
(TNT) obtained after anodization of CP Ti, Ti-6Al-4V, Ti-6Al-7Nb, Ti-13Nb-13Zr
and β-21S for 1 h in an electrolyte consisting of 1 M H 2 SO 4 and 0.08 M HF at
25 °C are shown in Fig. 13 (a–e). Highly ordered, regular and vertically aligned TNT
structures were observed on CP Ti, Ti-6Al-4V and Ti-6Al-7Nb as shown in Fig. 13a–
c. The metastable β alloy, Ti-13Nb-13Zr given in Fig. 13d showed the formation of
nanostructured dual morphology with varied pore diameters. In the same image,
a high degree of ordering in tubes was visible beneath the small porous structure.
On the contrary, beta alloy, beta-21S in Fig. 13e showed no sign of nanotubular
morphology due to composition of electrolyte solution used, whereas, the electrolyte
with 0.25 M NH 4 F in ethylene glycol reported the formation of nanotubular structure
[98]. At higher magnification (right side), random structure was observed. Thus,
at various compositions and at fixed parameters such as time (1 h), temperature
(25 °C) and electrolyte composition, titanium alloys exhibit significant properties.
529
8 Anodization of Titanium Alloys
Basically, titanium alloys are classified as α, near-α, α + β, metastable β, or stable β
depending upon the room temperature microstructure [87]. In this aspect, titanium
alloying elements can be classified as α-stabilizers (Al, O, N, C), β-stabilizers (Nb, V,
Ta, Fe Cr, Si, Co, Mn) and neutral such as Zr [72]. Titanium alloys are widely used in
hard tissue replacements in artificial bones, joints and dental prosthetic applications.
Various attractive properties of the Ti-based alloys such as high corrosion resistance,
exceptional mechanical properties and good biocompatibility were the driving force
for the early introduction of α (Cp-Ti) and α + β (Ti–6Al–4 V, Ti-6Al-7Nb) alloys
as well as the more recent development of modern and orthopaedic metastable β
Ti and β stabilized Ti alloys [16, 27]. Several studies reported the formation of
nanotubes on different Ti alloys [61, 88–94]. Nakada et al. [95] suggested using TiNb-Ta-Zr (TNTZ) alloy for orthopaedic implants because of its exceptional mechanical properties, biocompatibility and anticorrosion properties. In another study, an
anodized nanotube oxide layer with two size scale structures was reported on Ti28Zr-8Nb alloy using buffered electrolyte [96]. The influence of alloy composition
on the formed anodic oxide layer morphology on binary titanium alloys such as
Ti-xTa, Ti-yZr, and Ti–Al was investigated by the researchers [89, 97]. The study
revealed the formation of nanotube arrays on Ti-Zr alloy with a decreased diameter and increased tube length with increasing zirconium content. A tantalum oxide
(Ta 2 O 5 ) porous layer with pore diameter ranges from 2 to 35 nm on tantalum metal
can be formed electrochemically in acid-containing HF as electrolyte [98]. Highly
ordered Ta 2 O 5 nanoporous layer have grown on tantalum foils by anodization using
glycerol and NH 4 F containing electrolyte and it was found that average pore diameter
and thickness were affected by the NH 4 H concentration [99].
Anodization of CP Ti and titanium alloys (Ti-6Al-4 V, Ti-6Al-7Nb, Ti-13Nb13Zr, and β-21s) has investigated at optimized parameter [61]. FESEM images (left
side at lower and right side at higher magnifications) of anodic TiO 2 nanotube arrays
(TNT) obtained after anodization of CP Ti, Ti-6Al-4V, Ti-6Al-7Nb, Ti-13Nb-13Zr
and β-21S for 1 h in an electrolyte consisting of 1 M H 2 SO 4 and 0.08 M HF at
25 °C are shown in Fig. 13 (a–e). Highly ordered, regular and vertically aligned TNT
structures were observed on CP Ti, Ti-6Al-4V and Ti-6Al-7Nb as shown in Fig. 13a–
c. The metastable β alloy, Ti-13Nb-13Zr given in Fig. 13d showed the formation of
nanostructured dual morphology with varied pore diameters. In the same image,
a high degree of ordering in tubes was visible beneath the small porous structure.
On the contrary, beta alloy, beta-21S in Fig. 13e showed no sign of nanotubular
morphology due to composition of electrolyte solution used, whereas, the electrolyte
with 0.25 M NH 4 F in ethylene glycol reported the formation of nanotubular structure
[98]. At higher magnification (right side), random structure was observed. Thus,
at various compositions and at fixed parameters such as time (1 h), temperature
(25 °C) and electrolyte composition, titanium alloys exhibit significant properties.