Synthesis of self-organized mixed oxide nanotubes by sonoelectrochemical anodization of Ti–8Mn alloy

Self ordered arrays of titanium manganese mixed oxide nanotubes were prepared by anodization of Ti8Mn alloy (UNS R56080) under ultrasonication in diluted ethylene glycol containing fluoride. The dimensions of the nanotubes (diameter: 20–100 nm and length: 0.5–2.0 μm) could be tuned by changing the synthesis parameters. The as-anodized nanotubes showed a stoichiometry of (Ti,Mn)O2. Upon annealing at 500 °C in oxygen atmosphere, the nanotubes contained a mixture of anatase + rutile phases of TiO2 and Mn2O3. The composition of the oxide nanotubes was influenced by the chemistry of the phases present in the alloy. More manganese content was observed in the oxide formed on the β-phase than in the oxide layer of α-phase. Anodization in the ultrasonic field increased the kinetics of nanotubular oxide formation and resulted in homogeneous ordering of the nanotubular arrays as compared to the anodization by conventional stirring in the fluoride containing ethylene glycol solution. Whereas, anodization in aqueous acidified fluoride solutions resulted in severe attack of the β-phase and did not show presence of nanotubular oxide structure.