Porous Titanium Oxide Films Research Articles

Plasma electrolytic oxidation of Ti-6Al-4V alloy and its influence on the machinability during micro-milling

With the aim to modify the micro-milling behaviors of Ti6Al4V alloy for engineering application, a novel processing method of plasma electrolytic oxidation assisted micro-milling (PEOAM) was proposed in this paper. Ti6Al4V alloy was treated by plasma electrolytic oxidation (PEO) with an electrolyte mainly containing KH2PO4 and Ca(CH3COO)2, so that a low-strength oxide film that could be easily removed grew in-situ on the alloy surface. The oxide film was then subjected to micro-milling. The structure and composition of the oxide surface layer and sub-surface layer were characterized by scanning electron microscope and X-ray spectrometer. The cutting force of micro-milling applied to the oxide film was detected by dynamometer. Meanwhile, the milled surface roughness and top burrs were measured and analyzed by white light interferometer. The results indicated that PEO could promote the in-situ growth of 19 μm-thick loose and porous titanium oxide film on the surface of Ti6Al4V alloy. Compared with non-oxidation specimens, the microhardness and elastic modulus of the oxide surface layer were decreased by 34.5% and 47.1%, respectively. With the same micro-milling parameters, the cutting forces Fx and Fy were decreased by 51.4% and 71.4% respectively in down milling, and 36.2% and 88.4% in up milling. The surface roughness Ra was decreased by 26.7%.

On the Plasma-Electrolytic Formation of Porous Films of Titanium Oxide

In this work, the features of the formation of electrolyte plasma and its influence on the structure of the surface of Ti are investigated. It is revealed that the formation of plasma in the process of the anodic polarization of Ti in an aqueous solution of sulfuric acid leads to the formation of a porous oxide on the surface. It is shown that the porous nature of the formed oxide layers predetermine the specific behavior of the plasma. The topology of the surface of the formed porous titanium-oxide film is studied by scanning-electron- and atomic-force microscopy. It is established that the distribution of pores on the surface is of a complex stochastic nature and their maximum sizes did not are around 200–300 nm.

Reactivity of porous titanium oxide film and chitosan layer electrochemically formed on Ti-6Al-4V alloy in biological solution

Uniform porous TiO2 film on Ti-6Al-4V alloy was obtained by hard anodic oxidation and successfully the chitosan layer was electrodeposited. Surface morphology, compositional properties and diffraction patterns were analyzed by scanning electron microscopy with energy dispersive X-ray analysis system and X-ray diffraction. The reactivity of anodic porous TiO2 film in the presence or absence of chitosan layer was investigated by electrochemical methods in biological solution and compared with the reactivity with the unmodified Ti-6Al-4V alloy surface. The electrochemical impedance spectroscopy method was used to compare the response reactivity of the three surfaces. The combination of the high biocompatibility of chitosan and good mechanical characteristics of Ti-6Al-4V alloy make the obtained porous TiO2 film combined with chitosan a promising method to improve the reactivity of medical implants in biological solution.

Highly porous titania films coated on sub-micron particles with tunable thickness by molecular layer deposition in a fluidized bed reactor

Titanium alkoxide (titanicone) thin films were coated on large quantities of sub-micron sized silica particles at 100°C using molecular layer deposition (MLD) in a fluidized bed reactor. Titanium tetrachloride and ethylene glycol were used as precursors. The content of titanium on the particles increased linearly as the number of MLD coating cycles increased. The conformity of the films, with a thickness of ~12nm, was verified using TEM for silica particles coated with 50 cycles of titanicone. The composition of the titanicone films was confirmed using energy dispersive X-ray spectrometry. Porous titanium oxide films were formed for the particles coated with 50 cycles of titanicone MLD by oxidation in air at 400°C or by decomposition of the organic components of the titanicone films in the presence of water. The thicknesses of the films were reduced from ~12nm to ~8nm after oxidation in air at 400°C for 1hr. The effect of aging on the titanicone films was studied at different lengths of aging time in the presence of water. A greatly increased surface area of 48.8m2g−1 was obtained for the particles exposed to water for 24hr, compared to the as-deposited 50 cycles of titanicone coated sample with a surface area of 7.7m2g−1. The decomposition of titanicone films, after exposure to water vapor for various lengths of time, was studied using Fourier transform infrared spectroscopy.

Design of capillary flows with functionally graded porous titanium oxide films fabricated by anodization instability

We have developed an electrochemical fabrication method utilizing breakdown anodization (BDA) to yield capillary flows that can be expressed as functions of capillary height. This method uses anodization instability with high electric potentials and mildly acidic electrolytes that are maintained at low temperature. BDA produces highly porous micro- and nano-structured surfaces composed of amorphous titanium oxide on titanium substrates, resulting in high capillary pressure and capillary diffusivity. With this fabrication technique the capillary flow properties can be controlled by varying the applied electric field and electrolyte temperature. Furthermore, they can be expressed as functions of capillary height when customized electric fields are used in BDA. To predict capillary flows on BDA surfaces, we developed a conceptual model of highly wettable porous films, which are modeled as multiple layers of capillary tubes oriented in the flow direction. From the model, we derived a general capillary flow equation of motion in terms of capillary pressure and capillary diffusivity, both of which can be expressed as functions of capillary height. The theoretical model was verified by comparisons with experimental capillary flows, showing good agreement. From investigation of the surface morphology we found that the surface structures were also functionally graded with respect to the capillary height (i.e. applied electric field). The suggested fabrication method and the theoretical model offer novel design methodologies for microscale liquid transport devices requiring control over propagation speed.

Preparation of porous titanium oxide films onto indium tin oxide for application in organic photovoltaic devices

In this work, porous ordered TiO2 films were prepared through sol gel route by using a monolayer of polystyrene spheres as template on indium-tin oxide/glass substrate. These films were characterized by SEM, AFM, Raman spectroscopy, UV–vis absorbance and XRD. The UV–vis absorbance spectrum show a pseudo band gap (PBG) with maxima at 460nm arising from the light scattering and partial or total suppression of the photon density of states, this PBG can be controlled by the size of the pore. We also propose the use of this porous film as electron acceptor electrode in organic photovoltaic cells; we show that devices prepared with porous titania displayed higher efficiencies than devices using compact titania films as electrode. Such behaviour was observed in both bilayer and bulk heterojunction devices.

Porous TiO 2 film prepared by micro-arc oxidation and its electrochemical behaviors in Hank's solution

Porous titanium oxide film was prepared by micro-arc oxidation (MAO) method on the surface of titanium alloy in electrolyte containing Ca and P. Surface characterizations of the film were carried out using X-ray diffractometer (XRD), scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS) before and after immersion in Hank's solution. Electrochemical behaviors and corrosion resistance were studied by electrochemical techniques. The film was mainly composed of titania, α-tricalcium phosphate (α-TCP) and amorphous Ca–P compounds. α-TCP and amorphous compounds could transformed into hydroxyapatite (HA) when immersed in Hank's solution. MAO film showed higher corrosion potential and lower corrosion current than the titanium alloy and its chemical stability was slightly changed after formation of HA. Fitted electrochemical impedance spectroscopy (EIS) data indicated that after immersion for 2 weeks the MAO film kept good corrosion resistance. Porous TiO 2 film on titanium alloy by MAO method showed good chemical stability in Hank's solution and the transformation of Ca–P compounds into HA indicated that MAO was an effective method for preparing titanium alloys as bioactive artificial bone substitute even when Ca and P in the tissue environment were not abundant.

Formation of porous anodic titanium oxide films in hot phosphate/glycerol electrolyte

Abstract The present study reveals the formation of porous anodic films on titanium at an increased growth rate in hot phosphate/glycerol electrolyte by reducing the water content. A porous titanium oxide film of 12 μm thickness, with a relatively low content of phosphorus species, is developed after anodizing at 5 V for 3.6 ks in 0.6 mol dm −3 K 2 HPO 4 + 0.2 mol dm −3 K 3 PO 4 /glycerol electrolyte containing only 0.04% water at 433 K. The growth efficiency is reduced by increasing the formation voltage to 20 V, due to formation of crystalline oxide, which induces gas generation during anodizing. The film formed at 20 V consists of two layers, with an increased concentration of phosphorus species in the inner layer. The outer layer, comprising approximately 25% of the film thickness, is developed at low formation voltages, of less than 10 V, during the initial anodizing at a constant current density of 250 A m −2 . The pore diameter is not significantly dependent upon the formation voltage, being ∼10 nm.

3D Hierarchical Porous TiO2 Films from Colloidal Composite Fluidic Deposition

We use a “structure director” colloidal composite to fabricate porous titanium oxide films having a hierarchical pore architecture consisting of mesopores regularly distributed in the macropore shell. The colloidal composite consists of polystyrene beads coated with (ammonium lactate)titanium dihydroxide deposited by means of a fluidic technique. The pore properties and interconnections are controlled at different length scales: a macroscale, which is imposed by the polystyrene beads; a mesoscale, which is controlled by the composition and by the thermal history of the composite; a nanometer-scale, controlled by the nanocrystal sintering in air. Our approach can be extended to a wide class of water-soluble metal oxide precursors; therefore, it opens interesting perspectives for “bottom-up” nanotechnology of functional arrays and devices.

Effects of microstructure of anodic titania on the formation of bioactive compounds

To improve preferential nucleation of calcium phosphate by attractive interaction between Ca 2+ ion in biological fluid and titania surface, negatively charged porous titanium oxide films for implant applications were synthesized by electrochemical process in electrolyte of 1.5 M sulfuric acid containing phosphoric acid as an additive, and the effects of surface characteristics of anodic titania on the formation of bioactive apatite were investigated. More nucleation capability of bioactive Ca–P compound was shown on the anodic film formed in high concentration of phosphoric acid electrolyte compared with lower concentration of phosphoric acid. The incorporated phosphate species were found mostly in the forms of HPO 4 −, PO 4 −, and PO 3 −.