Fabrication parameter-dependent morphologies of self-organized ZrO2 nanotubes during anodization

Abstract

Zirconia (ZrO 2 ) nanotubes have been synthesized using a facile anodizing process in organic electrolyte systems containing a low content of fluoride. The nanotube architecture evolution was recorded at different anodization periods (1-24 h) by scanning electron microscopy. A compact layer was found between the Zr substrate and its upper tubular layer after 1 h of anodization, whereas after further anodization for 3 h the compact layer disappeared. Meanwhile, ZrO 2 nanotubes turned to a uniform structure from top to bottom. However, after 18-24-h-long anodization, the uniform tubular layer was replaced by a random layer composed of various structural defects. Since the compact layer was not completely dissolved, the retained compact layer yielded O-rings with double walls on the outer surface of the nanotubes.

Electrochemical synthesis of oxide nanotubes on Ti6Al7Nb alloy and their interaction with the simulated body fluid

“…This layer can be later removed by dissolving in water-containing electrolyte. This process was observed by Fang et al [33] who studied the nanotube evolution on Zr with time. They demonstrated that the compact layer rich in fluorine is formed between the metal and upper tubular layer after 1 h of anodization, and then, it disappears after 3 h. This experiment shows that the outer layer of nanotubes is fluoride-rich and it can be dissolved in the electrolyte.…”

Synthesis of ZrO2 nanotubes in inorganic and organic electrolytes by anodic oxidation of zirconium

“…After anodization, the samples had an amorphous structure which could be converted to tetragonal and monoclinic modifications after heating in a temperature range of 400-900°C. In their most recent study, Fang et al [34] followed an architecture evolution of nanotubes at different anodization points. They showed that while after 1 h, a compact layer rich in fluorine is formed between Zr and upper tubular layer, it disappears after 3 h. These results indicate that the outer layer of ZrO 2 nanotubes is fluoride-rich, and it can be dissolved in the surrounding electrolyte.…”

“…In the case of zirconia nanotubes, the amorphous structure limits their applications area as a catalyst and photocatalyst [34]. Amorphous structure demonstrates the lack of stability in a solution of low pH level.…”

“…Then, in order to control the microstructure and morphology of ZrO 2 layer being formed, the influence of a number of experimental parameters as a composition of the electrolyte [29][30][31], applied potential [32,33], anodization time [32], sweeping rate [30], or pH [30,32] was investigated. Also, aqueous and nonaqueous electrolytes were applied [4,6,27,28,33,34].…”

“…Muratore et al [38,39] and Fang et al [34] pointed out the possible influence of compact and thin fluoride-rich layer formed during anodization on the tubular structure formation.…”