Effect of heat treatments on apatite-forming ability of NaOH- and HCl-treated titanium metal

Titanium (Ti) metal was soaked in HCl solution after NaOH treatment and then subjected to heat treatments at different temperatures. Their apatite-forming abilities in a simulated body fluid (SBF) were discussed in terms of their surface structures and properties. The nanometer scale roughness formed on Ti metal after NaOH treatment remained after the HCl treatment and a subsequent heat treatment below 700°C. Hydrogen titanate was formed on Ti metal from an HCl treatment after NaOH treatment, and this was converted into titanium oxide of anatase and rutile phases by a subsequent heat treatment above 500°C. The scratch resistance of the surface layer increased with the formation of the titanium oxide after a heat treatment up to 700°C, and then decreased with increasing temperature. The Ti metal with a titanium oxide layer formed on its surface showed a high apatite-forming ability in SBF when the heat treatment temperature was in the range 500–700°C. The high apatite-forming ability was attributed to the positive surface charge in an SBF. These positive surface charges were ascribed to the presence of chloride ions, which were adsorbed on the surfaces and dissociated in the SBF to give an acid environment.     

Effect of heat treatment on apatite-forming ability of Ti metal induced by alkali treatment

The present authors previously showed that titanium metal forms a bone-like apatite layer on its surface in a simulated body fluid (SBF), when it has been treated with a NaOH solution to form a sodium titanate hydrogel layer on its surface. This indicates that the NaOH-treated Ti metal bonds to living bone. The gel layer as-formed is, however, mechanically unstable. In the present study, the NaOH-treated Ti metal was heat treated at various temperatures in order to convert the gel layer into a more mechanically stable layer. The gel layer was dehydrated and transformed into an amorphous sodium titanate layer at 400–500°C, fairly densified at 600°C and converted into crystalline sodium titanate and rutile above 700°C. The induction period for the apatite formation on the NaOH-treated Ti metal in SBF increased with the transformation of the surface gel layer by the heat treatment. Ti metal heat treated at 600°C, however, showed a fairly short induction period as well as high mechanical stability, since it was covered with a fairly densified amorphous layer.     

Effect of thermal treatment on apatite-forming ability of NaOH-treated tantalum metal

The prerequisite for an artificial material to bond to living bone is the formation of bonelike apatite on its surface in the body. This apatite can be reproduced on its surface even in an acellular simulated body fluid with ion concentrations nearly equal to those of the human blood plasma. The present authors previously showed that the tantalum metal subjected to a NaOH treatment to form a sodium tantalate hydrogel layer on its surface forms the bonelike apatite on its surface in SBF in a short period. The gel layer as-formed on the metal is, however, not resistant against abrasion, and hence thus-treated metal is not useful for clinical applications. In the present study, effects of thermal treatment on the mechanical properties and apatite-forming ability of the NaOH-treated tantalum metal were investigated. The sodium tantalate gel on the NaOH-treated tantalum was dehydrated to convert into amorphous sodium tantalate by a thermal treatment at 300 °C in air environment and into crystalline sodium tantalates by the thermal treatment at 500 °C. Resistivity of the gel layer against both peeling-off and scratching was significantly improved by the thermal treatment at 300 °C. The high apatite-forming ability of the sodium tantalate hydrogel was a little decreased by the thermal treatment at 300 °C, but appreciably decreased by the thermal treatment at 500 °C. It is believed that the tantalum metal subjected to the 0.5 M-NaOH treatment and the subsequent thermal treatment at 300 °C is useful as implants in dental and orthopaedic fields, since it shows high bioactivity as well as high fracture toughness. © 2001 Kluwer Academic Publishers     

Effects of oxygen content of porous titanium metal on its apatite-forming ability and compressive strength

Porous titanium metal subjected to NaOH and heat treatments is useful as a bone substitute as it shows high mechanical strength as well as osteoconductivity and osteoinductivity. However, the porous metal is liable to be contaminated with oxygen gas during the fabrication process and this incorporated oxygen could lead to adverse effects on the bioactivity and mechanical properties of the prepared porous body. In this study, oxygen contamination during fabrication of bioactive porous bodies was measured. It was found that the oxygen content of the titanium metal was increased from 0.08 to 0.23 mass% when the porous body was prepared from bar stock, and it further increased up to 0.51 mass% when it was subjected to NaOH and heat treatments. Despite this, the porous bodies subjected to NaOH and heat treatments formed apatite on their pore walls within 1 day in a simulated body fluid. This result was consistent with the apatite-forming ability of NaOH- and heat-treated titanium plates with different oxygen contents in the range of 0.05 to 0.30 mass%. The compressive strength of the porous body was increased about 10% by the NaOH and heat treatments.     

Effect of heat treatment on the structure of titanium dioxide films

The development of nanocrystalline phases during isothermal annealing of titanium dioxide films deposited by reactive magnetron sputtering at various rates onto silica glass substrates has been studied. It is established that the heat treatment at temperatures within 500–700°C in air or in vacuum leads to significantly different results, depending on the initial crystalline structure of as-deposited films.     

Transformation of microporous titanium glycolate nanorods into mesoporous anatase titania nanorods by hot water treatment

High surface area titanium glycolate microporous multi-faceted nanorods were synthesized from the reaction of titanium alkoxides (Ti(OEt)₄, Ti(O ⁱ Pr)₄, or Ti(O ⁿ Bu)₄) with ethylene glycol, using a sol–gel reflux method. The specific surface area of the as-synthesized titanium glycolate nanorods obtained from Ti(OEt)₄ is ~480 m²/g. A hot water treatment at 90 °C for 1 h transformed the titanium glycolate microporous nanorods into mesoporous anatase TiO₂ nanorods. The shape of the nanorods was conserved after hot water treatment and the microporous to mesoporous transformation took place without significant change in the surface area (477 m²/g). Micro Raman spectroscopy, scanning electron microscopy, transmission electron microscopy, X-ray diffraction, solid state NMR, and nitrogen adsorption/desorption were used to characterize the samples. As a demonstration of potential applications, the thus formed mesoporous anatase TiO₂ nanorods were tested for their photocatalytic efficiency in the degradation of crystal violet, and a photodegradation mechanism is proposed.     

Structure, morphology and fibroblasts adhesion of surface-porous titanium via anodic oxidation

Surface-porous titanium samples were prepared by anodic oxidation in H₂SO₄, H₃PO₄ and CH₃COOH electrolytes under various electrochemical conditions. X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX) were employed to characterize the structure, morphology and chemical composition of the surface layer, respectively. Closer analysis on the effect of the electrochemical conditions on pore configuration was involved. It can be indicated that porous titania was formed on the surface layer, and the pore configuration was influenced by electrolyte composition and crystal structure of the titania. The fibroblast cells experiment showed that anodic oxidation of titanium surface could promote fibroblast adhesion on Ti substrate. The results suggested that anodic oxidation of Ti in CH₃COOH was suitable to obtain surface-porous titanium oxides layers, which might be beneficial for better soft tissue ingrowths.     

Fabrication of titania nanocoatings on ZnS-type phosphors using titanium precursor modified by glacial acetic acid

In order to suppress fast degradation of ZnS-type phosphors applied in field emission displays (FEDs), the surface coating and encapsulation are expected to be an effective way. The titania nanocoatings are obtained by a sol-gel route using tetrabutyl titanate (TBT) as the precursor in this paper. With the addition of the glacial acetic acid (HAc), due to the formation of Ti(OC₄H₉)_x(Ac)_4 - x ligand, the hydrolysis process is inhibited. When the molar ratio of HAc to TBT is 2, the appropriate gelation rate is obtained. The coating process is perhaps related to the electrostatic forces and chemical bonding between ZnS phosphor and Ti(OH)₂(Ac)₂ ligand.     

Electrochemical examination of surface films formed during chemical mechanical planarization of copper in acetic acid and dodecyl sulfate solutions

Electrochemical impedance spectroscopy (EIS) is employed to study the competitive reactions of surface corrosion and passivating film formation on a Cu-rotating disc electrode (RDE) in pH-adjusted solutions of H₂O₂, acetic acid (HAc) and ammonium dodecyl sulfate (ADS). The surface reactions that occur at the open circuit potential of this system are relevant for chemical mechanical planarization (CMP) of Cu-interconnect structures. The results show how the discontinuous film of Cu-oxides formed by H₂O₂ acts both to dissolve (via reactions with HAc) and to passivate the Cu surface. The relatively more continuous ADS film serves as a dissolution suppressor and regulates the removal of Cu/Cu-oxide surface layers. The results presented here also demonstrate the utility of EIS involving RDEs to design slurry chemistries for Cu-CMP.     

The duplex nature of anodic barrier films formed on aluminium in aqueous borate and borate-glycol solutions

Direct transmission electron microscopy of ultramicrotomed sections of aluminium and its anodic films formed in borate-containing environments, and subsequent electron-beam-induced crystallization, has been employed to gain further insight into the development of contaminated Al₂O₃ during anodizing. For film formation in ammonium pentaborate solution, it is suggested that borate species incorporated into the Al₂O₃ film material are immobile during anodizing. Conversely, the borate species incorporated into the film material during anodizing in the ammonium pentaborate-ethylene glycol electrolyte are apparently mobile in the field. Thus, on a direct interpretation basis, the apparent aluminium transport number can be assessed from the extents of the differently textured regions apparent after electron-beam-induced crystallization in which the borate species are immobile.     

Multilayer structure of tantalum anodic oxide films formed in dilute phosphoric acid

An investigation has been made of the multilayer structure of anodic oxide films on pure tantalum, formed up to various voltages with a constant current density of 1.0 mA cm^-2 in 1.0 × 10^-2 N H₃PO₄ at 20°C. For the study, infrared reflectance spectra (IRRS) were recorded and the optical thickness measuring method was successfully applied using the wavelengths of optical interference maxima and a chemical film stripper (concentrated ammonium hydrogen difluoride aqueous solution).The conclusions are that: (1) tantalum anodic oxide films anodized in dilute phosphoric acid consist of three layers, irrespective of the formation voltage; (2) the innermost layer is uniform whatever the anodization voltage; (3) phosphate anions are incorporated in both the outermost and middle layers but not in the innermost layer; (4) all three layers grow from the initial formation stage and the growth rates are nearly equal; (5) for formation voltages below 100 V the middle layer has an unchanging chemical structure, but above 100 V its chemical structure changes with the voltage; (6) the outermost layer appears to vary in chemical structure over all anodization voltages.     

Surface characteristics and bioactivity of oxide film on titanium metal formed by thermal oxidation

In this study, we characterized the surface of oxide film formed on titanium metal through the use of thermal treatment and investigated the effect of surface characteristics on the bioactivity of titanium. The as-received sample group was prepared by polishing and cleaning CP-Ti as a control group, and thermally oxidized sample groups were prepared by heat treating at 530, 600, 700, 800, 900, and 1000°C respectively. Micro-morphology, crystalline structure, chemical composition, and binding state were evaluated using FE-SEM, XRD, and XPS. The bioactivity of sample groups was investigated by observing the degree of calcium phosphate formation from immersion testing in MEM. The surface characterization tests showed that hydroxyl group content in titanium oxide film was increased, as the density of titanium atoms was high and the surface area was large. In MEM immersion test, initial calcium phosphate formation was dependent upon the thickness of titanium oxide, and resultant calcium phosphate formation depended on the content of the hydroxyl group of the titanium oxide film surface.     

Effect of titanium and titania on chemical characteristics of hydroxyapatite plasma-sprayed into water

HA and its composite particles (HA/Ti, HA/TiO₂) were plasma-sprayed into water as well as on the Ti substrate, respectively. The microstructure and phase compositions of the sprayed HA and its composite particles before and after impinging on the substrate were studied by using scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier transform infrared (FTIR) spectroscopy. The results showed that the HA in the composite particles sprayed into water had a higher crystallinity than that in the composite coating. The addition of Ti or TiO₂ could both influence the decomposition of HA, but no chemical reacting product between them was formed before and after impinging on the substrate. However, EDS analyses showed the occurrence of interdiffusion of elements between HA and TiO₂, which was favorable to enhance the cohesive strength of particles in the composite coating. The post heat treatment at 650 °C for 2 h can effectively improve the crystallinity of coating by transforming amorphous phases into HA.     

Effect of the heat treatment on the morphology and sorption ability to metal ions of metallurgical slag

The effect of the phase composition of metallurgical slag on its ability to adsorb copper ions from aqueous solutions has been investigated. Granulated slag samples, mainly amorphous, have been pre-heated at 400, 600, 800 and 1000°C, then cooled slowly in the absence of moisture. Above 600°C crystallisation of a mineral gehlenite of the melilite group and of calcium silicates of the Ca₂SiO₄ structure type begins. The appearance of crystalline phases facilitates exchange and adsorption and the amount of copper adsorbed per a gram slag increasing about 2–4 times. The important role of the crystalline phases in the slag permits the synthesis of new materials adsorbing heavy metal ions on the basis of controlled liquid slag crystallization.     

Dielectric and structural characteristics of Ta2O5 anodic films formed in phosphoric acid electrolytes

The duplex nature of Ta₂O₅ films formed in H₃PO₄ electrolytes with different concentrations has been chanyotarired by net weight gain measurements of the films during the anodic oxidation, as well by capacitance and etch-rate measurements of the oxide films. The density and permittivity of each layer of the films formed in different concentrations of the electrolyte have been calculated.     

Development of an optical model for steady state porous anodic films on aluminium formed in phosphoric acid

Porous anodic oxide films on aluminium formed in phosphoric acid (PAA) have been characterized nondestructively by spectroscopic ellipsometry. Compared to previous studies on porous films formed in sulfuric acid, the optical behaviour of PAA films reveals new features which have been attributed to film-substrate interface roughness and optical anisotropy effects. On one hand relatively large interface roughness has been simulated by a graded index model. On the other hand, the implementation of uniaxial anisotropy in the optical model of the PAA film enables to interpret spectroscopic ellipsometry data acquired at multiple angles of incidence in terms of the morphology of the films. More specifically, accurate and physically realistic values are found for the porosity and porous film thickness. Although more difficult to interpret from the optical findings, the thickness of the barrier part of the porous film can also be estimated. The ellipsometry characterizations are confirmed by complementary TEM analysis of various films. Finally, the anisotropy exhibited by the PAA films is in line with recent theoretical predictions of the optical behaviour of arrays of parallel cylindrical capillaries in an isotropic medium proposed by other authors.     

Raman spectroscopy study of the phase transformation on nanocrystalline titania films prepared via metal organic vapour deposition

Raman spectroscopy (RS) was used to study the phase transformations of nanocrytalline TiO₂ thin films. The films were grown by a vertical-flow cold-wall metal organic chemical vapour deposition system, using Ti(C₁₀H₁₄O₅) as the source reagent, at different substrate temperatures. The results indicate that the anatase phase is present at around 550 °C and the rutile phase starts to form at 620 °C. The anatase phase completely transforms into the rutile phase at 680 °C. We have demonstrated that RS can be used as a powerful nondestructive technique for a quick and efficient determination of the phase of TiO₂ thin films.     

Effect of the precursor heat treatment procedure on the properties of titania photocatalysts

We have studied the effect of heat treatment of titanium dioxide nanopowders prepared by autoclaving peroxo titanic acid gel at 130°C and refluxing it on their structural properties and catalytic activity for methylene blue degradation. Titanic acid precipitated from an aqueous titanyl sulfate solution by ammonia was used as a precursor for the synthesis of the peroxo titanic acid gel. Residual ammonium complexes and peroxide groups, whose concentration was determined by the peroxo titanic acid gel heat treatment procedure, were shown to influence the adsorptive and catalytic properties of the titanium dioxide.     

Multifunctional porous titanium oxide coating with apatite forming ability and photocatalytic activity on a titanium substrate formed by plasma electrolytic oxidation

Plasma electrolytic oxidation (PEO) was used to make a multifunctional porous titanium oxide (TiO₂) coating on a titanium substrate. The key finding of this study is that a highly crystalline TiO₂ coating can be made by performing the PEO in an ammonium acetate (CH₃COONH₄) solution; the PEO coating was formed by alternating between rapid heating by spark discharges and quenching in the solution. The high crystallinity of the TiO₂ led to the surface having multiple functions, including apatite forming ability and photocatalytic activity. Hydroxyapatite formed on the PEO coating when it was soaked in simulated body fluid. The good apatite forming ability can be attributed to the high density of hydroxyl groups on the anatase and rutile phases in the coating. The degradation of methylene blue under ultraviolet radiation indicated that the coating had high photocatalytic activity.     

Fracture of anodic oxide formed on aluminium in sulphuric acid

Journal of Materials Science Letters -