TiO(2) is one of the most studied compounds in materials science. Owing to some outstanding properties it is used for instance in photocatalysis, dye-sensitized solar cells, and biomedical devices. In 1999, first reports showed the feasibility to grow highly ordered arrays of TiO(2) nanotubes by a simple but optimized electrochemical anodization of a titanium metal sheet. This finding stimulated intense research activities that focused on growth, modification, properties, and applications of these one-dimensional nanostructures. This review attempts to cover all these aspects, including underlying principles and key functional features of TiO(2), in a comprehensive way and also indicates potential future directions of the field.

TiO2 nanotubes: synthesis and applications.

Significance of calcium phosphate coatings for the enhancement of new bone osteogenesis – A review ☆

This paper reviews the state of the art of anodized titanium dioxide nanotubes (TiO2 NTs), with an emphasis on the growth mechanism leading to their formation and the effect of heat treatment on their structure and properties. The discussion is primarily focused on TiO2 NTs grown in fluoride containing electrolytes, although the mechanism of formation of NTs in fluoride free solutions via Rapid Breakdown Anodization (RBA) is briefly covered. After an initial overview of progress made on the synthesis of anodized TiO2 NTs the review provides an analysis of the factors affecting the anodizing process (fluoride concentration, electrolyte type, applied potential and anodizing time). Details of the current-time transient, the chemistry of the process and the chemical composition of the anodic films are described which provide key information to unveil the nanotube growth mechanism. The main debate is whether NTs growth in fluoride containing solutions occurs via field-assisted plastic flow (i.e. a constant upward displacement of the oxide to form the NTs) combined with field-assisted ejection of the Ti4+ ions (i.e. ions are ejected into the electrolyte without oxide formation) or via field-assisted dissolution (i.e. preferential dissolution at the pore base where the field is stronger) or whether both processes play a role. Whenever anodization takes place in organic solutions the experimental evidence supports the plastic flow model, whereas in aqueous media field-assisted (and chemical) dissolution occur. The mechanism of rib formation on the walls of the NTs is also reviewed, and it clearly emerges that the applied potential and water content in the electrolyte are key factors in determining whether the NTs are ribbed or smooth. There also appears to be a relationship between the presence of ribs and the evolution of oxygen bubbles at the anode. The impact of thermal treatment on the properties of the NTs is also described. A variety of crystalline structures are present in the NTs (i.e. anatase or rutile), depending on the heat treatment temperature and atmosphere and the resulting electrical properties can be varied from dielectric to semi-metallic. A heat treatment temperature limit ranging from 500 to 800 °C exists, depending on preparation history, above which sintering of nanoscale titania particles occurs leading to collapse of the NTs structure. Future work should aim at using annealing not just to influence the resulting crystalline phase, but also for generating defects to be exploited in specific applications (i.e. photocatalysis, water splitting and photovoltaics).

/pdf/a-review-of-growth-mechanism-structure-and-crystallinity-of-2ov7whusr1.pdf

A review of growth mechanism, structure and crystallinity of anodized TiO2 nanotubes

Lixia Sang,† Yixin Zhao,‡ and Clemens Burda* †Key Laboratory of Enhanced Heat Transfer and Energy Conservation, Ministry of Education and Key Laboratory of Heat Transfer and Energy Conversion, Beijing Municipality, College of Environmental and Energy Engineering, Beijing University of Technology, Beijing 100124, China ‡School of Environmental Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240, China Center for Chemical Dynamics and Nanomaterials Research, Department of Chemistry, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, Ohio 44106, United States

TiO2 nanoparticles as functional building blocks.

The review is focused on the latest achievements in the field of plasma-assisted fabrication of biocompatible CaP-based coatings for medical implants with the emphasis on the coatings composition, structure, mechanical and biological performance. The discussed properties of biocompatible CaP coatings have been recently prepared using the most frequently applied plasma-assisted techniques such as plasma spraying (PS), radio-frequency (RF) magnetron sputtering, pulsed laser deposition (PLD), and ion beam-assisted deposition (IBAD). The review shows that plasma-assisted fabrication allows us to prepare dense, homogeneous, pore-free and high adherent biocompatible coatings able to prevent the leaching of toxic ions from metal to the surrounding tissues or rough and porous coatings capable of stimulating osteogenesis of a new bone. The main advantages and limitations of the described techniques of CaP-based coatings fabrication are presented as well as the most important challenges and critical issues are highlighted.

https://portal.tpu.ru/SHARED/s/SURMENEV/nauka/Tab/2012_Review_Surmenev%20-%2016_final.pdf

A review of plasma-assisted methods for calcium phosphate-based coatings fabrication

The present paper describes a new method utilizing rapid anodization to quickly synthesize high-quality, high aspect ratio, robust titanium dioxide nanotube powders. TiO2 nanotube powders, with a typical nanotube outer diameter of approximately 40 nm, wall thickness of approximately 8−15 nm, and length of about 10−35 μm, were synthesized by potentiostatic rapid breakdown anodization of titanium foils in aqueous electrolytes of 0.3 M NaCl or 0.1 M HClO4 under an applied potential of 20 V. High reactivity and ultrahigh reaction rate are cornerstones responsible for periodic release of TiO2 nanotubes into solution and formation of a white precipitate of TiO2 nanotubes. The reaction yield is approximately 4−6 g in less than 3 h, and the approximate cost of the material is $3.50/g, based on the laboratory-scale production. Various characterization techniques, including FESEM, HRTEM, EDX, XRD, XPS, FT-IR, UV−visible diffuse-reflectance, and N2 adsorption, have been used to probe morphology, microstructure, crys...

A Novel Method for Synthesis of Titania Nanotube Powders using Rapid Breakdown Anodization

Electrochemical synthesis of silica-doped high aspect-ratio titania nanotubes as nanobioceramics for implant applications

Abrasive wear behavior of sprayed hydroxyapitite coatings by gas tunnel type plasma spraying

Microstructure and hardness properties of cermet coating sprayed by low power plasma

Vertically-oriented high aspect ratio titania nanotube bundles have been grown by a potentiostatic anodization of titanium sheet in fluoride-free electrolytes. The anodization conditions like the applied voltage were optimized for the synthesis of titania nanotubes in HClO4 and NaCl electrolyte. The resulting nanotubes have a length of about 30 microm, outer diameter about 40 nm, inner pore size of about 10 nm and the aspect ratio was 750:1 by anodization in 0.1 M perchloric acid of pH approximaately 1 at applied voltage of 20 V. While for nanotubes prepared in 0.3 M NaCl of pH 4.3, the length was above 50 microm with the aspect ratio of 1250:1. A method to increase the uniformity of nanotube was demonstrated by pretreatment the titanium sheet by (4 wt% HF + 5 M HNO3) solution prior to anodization. Titania nanotubes were prepared, for the first time, by anodization in aqueous H2SO4 electrolyte alone with tube length above 500 nm. Annealing studies were performed, on high aspect ratio Titania nanotube layers produced in HClO4 electrolyte, in the temperature interval of 300 to 550 degrees C. The XRD patterns and TEM data confirmed the formation of single anatase phase after annealing at 450 degrees C with perfect nanoubular structure. While the rutile titania phase starts to emerege after annealing at about 500 degrees C and the evidence for the appearance of rutile phase due to the oxidation of the underlying Ti metal at the interface between nanotube/Ti-metal was given. On the other hand, the nanotubular structure starts to destroy upon annealing temperature of approximate 550 degrees C by tube flattening and losing of roll-up characteristics as indicated in SEM images. The superior morphology of these high aspect ratio nanotubes and their rapid growth rate foreshadow a bright future in wide applications like dye-sensitized solar cells, water photolysis and nanobiomedical.

Narges F. Fahim

Papers

A Novel Method for Synthesis of Titania Nanotube Powders using Rapid Breakdown Anodization

Electrochemical synthesis of silica-doped high aspect-ratio titania nanotubes as nanobioceramics for implant applications

Abrasive wear behavior of sprayed hydroxyapitite coatings by gas tunnel type plasma spraying

Microstructure and hardness properties of cermet coating sprayed by low power plasma

Electrochemical growth of vertically-oriented high aspect ratio titania nanotubes by rabid anodization in fluoride-free media.