Effect of annealing on the phase transition and morphology of Ag NPs on/in TiO2 rods synthesized by a polyol method

In this study, we report the effect of annealing (250–700 ^oC) on the phase transition and morphology of silver (Ag) nanoparticles (NPs) on/in titanium dioxide (TiO₂) rods prepared using a polyol method. The annealed samples showed not only morphological change, i.e., a solid-to-liquid (melting) transition of Ag NPs due to its partial dissolution into the TiO₂ rods, but also early stage anatase crystallization and anatase–rutile transformation of TiO₂ rods under low annealing temperatures. Such findings, together with XRD and FE-SEM analyses, confirm that, upon higher annealing treatment, diffusion and coalescence leads to changes in the size and shape of the metal particles not only in the outermost regions, but also a random distribution and progressive growth of Ag clusters in the inner interface region. Here, it was shown that annealing can induce changes in morphology, as well as the chemical state and structure of Ag–TiO₂. The present polyol-synthesized Ag–TiO₂ composite also showed improved thermal stability.     

Spontaneously ordered TiO2 nanostructures

Titanium dioxide thin films were deposited on quartz substrates kept at different O₂ pressures using pulsed laser deposition technique. The effects of reactive atmosphere and annealing temperature on the structural, morphological, electrical and optical properties of the films are discussed. Growth of films with morphology consisting of spontaneously ordered nanostructures is reported. The films growth under an oxygen partial pressure of 3 × 10⁻⁴ Pa consist in nanoislands with voids in between them whereas the film growth under an oxygen partial pressure of 1 × 10⁻⁴ Pa, after having being subjected to annealing at 500 °C, consists in nanosized elongated grains uniformly distributed all over the surface. The growth of nanocrystallites with the increase in annealing temperature is explained on the basis of the critical nuclei-size model.     

The growth of interfacial compounds between titanium dioxide and bismuth oxide

The growth of interfacial compounds between TiO₂ and Bi₂O₃ during transient liquid phase bonding at 900, 1000 and 1100 °C for various times was investigated. The microstructures and compositions of compounds in joints were analyzed by means of SEM and EPMA. It was found that the compound Bi₄Ti₃O₁₂ forms initially and replaces the Bi₂O₃ interlayer. Bi₂Ti₄O₁₁ then arises at the interface between Bi₄Ti₃O₁₂ and TiO₂ and the metastable Bi₂Ti₂O₇ phase appears last at the interface between Bi₄Ti₃O₁₂ and Bi₂Ti₄O₁₁. The modes and activation energies of the growth of Bi₄Ti₃O₁₂ and Bi₂Ti₄O₁₁ were determined respectively. Holes in the middle of the joint heated at 1100 °C for 24 h were also found.     

Synthesis and characterization of Fe doped titanium dioxide nanopowders

Titanium dioxide nanopowders, doped with different amounts of Fe³⁺ ions (0.3-5 mass%), were synthesized by acid-catalyzed sol-gel method in a non-aqueous medium. The obtained powders were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy and determination of izoelectric points as well as particle diameters. Careful investigation of porous structure was provided by application of nitrogen adsorption-desorption method. Structure analysis showed that the obtained nanopowders exhibited the anatase crystal structure, independent of the amount of iron dopants. The presence of Fe³⁺ ions in anatase decreases the value of isoelectric point of undoped TiO₂. Unlike crystal structure, porosity parameters are strongly affected by the amount of iron ions incorporated in TiO₂ lattice. The mesoporosity of TiO₂ can be successfully controlled by changing the amount of iron dopants.     

Reaction synthesis of several titanium oxides through electrical wire explosion in air and in water

An experimental method to synthesize titanium oxide (Ti–O) through electrical wire explosion was performed. In this study, one experiment was conducted in air atmosphere, and the other with the wire fully dipped in distilled water. In air atmosphere, TiO₂ in anatase and rutile phases with ultrafine spherical particles was recovered. In distilled water, conversely, nanosized Ti–O material was recovered from an unknown phase, possibly a special phase of TiO₂ or a different type of titanium oxide such as Ti_nO or Ti_nO_2n−1. Recovered powders were analyzed using Scanning Electron Microscopy (SEM), High-resolution Transition Electron Microscopy (HR-TEM) and X-ray Diffraction (XRD) techniques.     

Simple fabrication of rod-like N-doped TiO2/Ag with enhanced visible-light photocatalytic activity

Rod-like N-doped TiO₂/Ag composites were successfully synthesized by a modified sol–gel method, without adding any surfactants. The entire preparation differs from the traditional sol–gel synthesis of TiO₂ that the reaction can get controlled by adjusting the flow speed of water vapor and NH₃. Characterization results show that as-prepared samples were uniform nanorods with an average length of ca. 3 µm and a cross section diameter of ca. 150 nm. The rod-like structure was formed during the annealing process. A possible mechanism was proposed to illustrate the formation of rod-like Ag–N–TiO₂. The degradation of methylene blue performed under visible light with the prepared nanorods as the photocatalyst demonstrated the photocatalytic activities of TiO₂ can be improved by the synergistic effect of N doping and Ag modification. In addition, as-prepared TiO₂-based photocatalyst exhibits a significantly enhanced photo-chemical stability after 5 catalytic cycles mainly due to the rod-like morphology. This indicated that they have some potential value in practical application.     

An in situ study of the deposition of a calcium phosphate mineralized layer on a silicon-substituted hydroxyapatite sensor modulated by bovine serum albumin using QCM-D technology

The deposition of a calcium phosphate (Ca-P) mineralized layer on Si-HA surface (the blank group, Au and the control group, HA) with and without BSA preadsorption was observed in real time using a quartz crystal microbalance with dissipation (QCM-D) technique. The effect of silicon doping on the adsorption of BSA onto a HA sensor was investigated. Approximately 1.5-fold more BSA adsorbed onto HA than Si-HA, indicating the inhibition of BSA adsorption onto the HA sensor by silicon doping. The decreasing ΔD_sat/Δf_sat value in the plots of ΔD–Δf versus adsorption time was predominantly attributed to BSA adsorption, and the decreasing ΔD value with adsorption time during adsorption equilibrium could be explained by the structural rearrangement of BSA on different substrates. Specifically, BSA preadsorption could be a trigger for the formation of nucleation sites for the mineralized layer, promoting nucleation but inhibiting growth. The growth rate was greater on bare substrates than on BSA adsorption substrates. The growth rate of the mineralized layer on the adsorbed BSA layer depended on the substrates in the following manner: Au>Si-HA>HA. The morphology of the mineralized layer depended on the surfaces, and a greater number and a more uniform distribution of smaller nanoparticles were observed on surfaces with preadsorbed BSA. Therefore, BSA could modulate the growth of the mineralized layer at the interface, which is advantageous for fabricating advanced biomaterials.     

Preparation of photocatalytic TiO2 coatings by gel-dipping with polysaccharides

Commercial tiles are being produced in vast quantities. The main properties of tiles are well established but there is an increasing interest in producing ceramics with tailored-properties and advanced functionalities. One way of adding value to commercial tiles is to deposit a photocatalytic coating to obtain ‘smart’ tiles for environmental reasons, e.g. for the (photo) degradation of organic pollutants in air or in a liquid. Here, we show the manufacture of ‘smart’ tiles by formation of TiO₂ coatings onto commercial tiles by a colloidal processing route based on the immersion of the substrate into a homogeneous aqueous ceramic suspension and its consolidation by agar thermogelation. The effect of the processing parameters (withdrawal rate, solid loading and gelling agent content) and the grain size on the photocatalytic activity of the final coated tiles is reported and discussed. Final coatings properties depend on the viscosity of the suspension, particle size, withdrawal rate, solid loading and gelling agent content, and hence, this dependence affects the photocatalytic activity of the coatings.     

Shock-consolidated TiO2 bulk with pure anatase phases fabricated by explosive compaction using underwater shockwave

Titanium dioxide (TiO₂) bulk with pure anatase phases was fabricated by an explosive compaction technique using an underwater shockwave. Dynamic shock pressure of 6 GPa was used to consolidate anatase TiO₂ powders. Its microstructural, crystalline structural and photocatalytic characteristics were observed and measured by various techniques, such as X-ray diffraction (XRD), scanning electron microscopy (SEM) and photocatalytic activity measurement system. It was confirmed that the relative density of anatase TiO₂ compact is about 96% (3.73 g/cm³) of the theoretical density (3.89 g/cm³) and a strong surface bonding between particles is formed by a shock energy. In X-ray diffraction analysis, high purity anatase phases, broadened peaks due to lattice defects and decreased crystallite size were found. For the photocatalytic activities, the anatase TiO₂ compact was quite excellent compared to the commercial sintered TiO₂ bulk.     

Formation of TiO2 nano fibers on a micro-channeled Al2O3-ZrO2/TiO2 porous composite membrane for photocatalytic filtration

In this study, needle-shape TiO₂ fibers were successfully fabricated inside a micro-channeled Al₂O₃-ZrO₂ composite porous membrane system using sol-gel method. The micro-channeled Al₂O₃-ZrO₂ composite was fabricated using the fibrous monolithic (FM) process. Pure anatase phase TiO₂ was crystallized from the as-coated amorphous phase during calcination at 510 °C. The TiO₂ fibers grew on the surface frame of the micro-channeled Al₂O₃-ZrO₂ composite membrane and fully covered the inside of the micro-channeled pores. The specific surface area of the TiO₂ coated membrane system was dramatically increased by over 100 fold compared to that of the non-coated system. The photocatalytic activity of the membrane was also assessed and was shown to very effectively convert organic materials. Thus, this novel membrane holds promise for use as an advanced filtration system.     

Effect of pre-nitridation treatment on the formation of anatase TiO2 films by anodization

High performance-anatase TiO₂ films were successfully formed on metallic titanium by anodization in an acidic electrolyte composed of H₂SO₄, H₃PO₄ and H₂O₂ subsequent to pre-nitridation treatment. The pre-nitridation treatment was carried out by pre-annealing metallic titanium under a nitrogen atmosphere of 0.1 MPa. The anodized films showed photocatalytic activity in photooxidization of the iodide anion into the tri-iodide anion. The nitridation treatment had a significant effect not only on the formation of anatase TiO₂ films but also on the photocatalytic activity of the anodized films.     

Microstructure refinement of alumina: Optimisation by gas pressure sintering process

This paper investigates densification and grain growth evolutions during gas pressure sintering of alumina. Isothermal sintering runs are performed under different nitrogen pressures: atmospheric pressure and 2 MPa. Experimental data are fitted thanks to constitutive laws in order to understand nitrogen pressure effect on densification and grain growth mechanisms of a fine-grained alumina. An optimal run of densification is proposed as an application of these results.     

Deposition behavior and characteristics of hydroxyapatite coatings on Al2O3, Ti,and Ti6Al4V formed by a chemical bath method

A simple chemical bath method was used to deposit hydroxyapatite (HA) coatings on Al₂O₃, Ti, and Ti6Al4V substrates at ambient pressure by heating to 65–95 °C in an aqueous solution prepared with Ca(NO₃)₂·4H₂O, KH₂PO₄, KOH, and EDTA. The deposition behavior, morphology, thickness, and phase of the coatings were investigated using scanning electron microscopy and X-ray diffractometry. The bonding strength of the coatings was measured using an epoxy resin method. The HA coatings deposited on the three kinds of substrates were fairly dense and uniform and exhibited good crystallinity without any additional heat treatment. A coating thickness of 1–1.8 μm was obtained for the samples coated once. By repeating the coating process three times, the thickness could be increased to 4.5 μm on the Al₂O₃ substrate. The bonding strength of these coatings was 18 MPa.     

A kinetic study on the electrophoretic deposition of hydroxyapatite–titania nanocomposite based on a statistical approach

In the present study, the electrophoretic deposition (EPD) process of hydroxyapatite–titania nanocomposite was kinetically described by the use of response surface methodology (RSM). The electrostatic interaction between particles in ethanol based suspensions was determined by Zeta potential and particle size analyses. After successful electrophoretic deposition from hydroxyapatite–titania suspensions with 0, 10 and 20 wt% of titania nanoparticles, it was shown that Baldisserri model can well reproduce the experimental data among the other semi-empirical kinetic equations. The as-deposited hydroxyapatite–titania nanocomposites were characterized employing SEM, AFM, XRD, and FT-IR analyses. Then, the effects of deposition voltage, deposition time and wt% TiO₂ on the kinetic of EPD at two time intervals (10–60 s and 60–300 s) were identified and quantified via RSM based on a central composite design (CCD). According to the results obtained from the statistical analysis, it was found that the deposition rate decreases by an increase in wt% TiO₂ and time. Also, a transition in deposition mechanism from linear to parabolic mode was observed and two second order polynomial equations were fitted to the response (deposit weight) at each time intervals.     

Investigation on mechanochemical synthesis of Al2O3/BN nanocomposite by aluminothermic reaction

Alpha-alumina–boron nitride (α-Al₂O₃–BN) nanocomposite was synthesized using mixtures of aluminum nitride, boron oxide and pure aluminum as raw materials via mechanochemical process under a low pressure of nitrogen gas (0.5 MPa). The phase transformation and structural evaluation during mechanochemical process were investigated by X-ray diffractometry (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and differential thermal analysis (DTA) techniques. The results indicated that high exothermic reaction of Al–B₂O₃ systems under the nitrogen pressure produced alumina, aluminum nitride (AlN), and aluminum oxynitride (Al₅O₆N) depending on the Al value and milling time, but no trace of boron nitride (BN) phases could be identified. On the other hand, AlN addition as a solid nitrogen source was effective in fabricating in-situ BN phase after 4 h milling process. In Al–B₂O₃–AlN system, the aluminothermic reaction provided sufficient heat for activating reaction between B₂O₃ and AlN to form BN compound. DTA analysis results showed that by increasing the activation time to 3 h, the temperature of both thermite and synthesis reactions significantly decreased and occurred as a one-step reaction. SEM and TEM observations confirmed that the range of particle size was within 100 nm.     

Biomimetic deposition of hydroxyapatite on the surface of silica thin film covered steel tape

The biomimetic deposition of hydroxyapatite (HA) on the surface of SiO₂ thin film coated metal substrates was developed and investigated.     

TiO2 as a sintering additive for KNbO3 ceramics

Improved densification during the conventional sintering of KNbO₃ ceramics was achieved by using small additions of TiO₂. This improved densification can be explained on the basis of high-temperature chemical reactions in the system. X-ray diffractometry and electron microscopy were used in combination with diffusion-couple experiments in order to elucidate the chemical reactions between KNbO₃ and TiO₂. TiO₂ reacts with KNbO₃ forming KNbTiO₅, and a low concentration of Ti incorporates in the KNbO₃ structure resulting in the formation of oxygen vacancies and, consequently, in an improvement in the densification. At ∼1037 °C eutectic melting between the KNbO₃ and the KNbTiO₅ further improves the densification of the KNbO₃ ceramics.     

In situ preparation of SiC/Si3N4-NW composite powders by combustion synthesis

Large-scale composite powders containing silicon carbide (SiC) particles and silicon nitride nanowires (Si₃N₄-NWs) were synthesized in situ by combustion synthesis (CS). In this process, a mixture of silicon, carbon black, polytetrafluoroethylene (PTFE) and a small amount of iron powders was used as the precursor. The products were characterized by XRD, SEM, EDS and TEM. The particles are equiaxed with diameters in the micron range, and the in situ formed nanowires are straight with uniform diameters of 20-350 nm and lengths of tens of microns. The Si₃N₄-NWs are characterized to be α-phase single crystals grown along the [1 0 1] or [1 0 0] direction. VLS and SLGS processes are proposed as the growth mechanisms of the nanowires. The as-synthesized powders have great potential for use in the preparation of high-performance SiC/Si₃N₄-NW composites.     

Aerosol assisted chemical vapour deposited (AACVD) of TiO2 thin film as compact layer for dye-sensitised solar cell

Compact TiO₂ has been introduced onto the surface of an indium tin oxide glass slide (ITO), using an aerosol-assisted chemical vapour deposition method. This serves as a blocking layer for a dye-sensitised solar cell (DSSC). The thickness of the compact TiO₂ could be controlled by deposition time. X-ray diffraction and Raman spectroscopy analyses reveal that the compact TiO₂ is made up of mixed anatase and rutile phases. The field emission scanning electron microscopy image displays a pyramidal morphology of the compact TiO₂. A layer of P25 paste was then smeared onto the compact TiO₂-modified ITO, using the doctor's blade method. A post-treatment procedure was applied to remove the contaminants from the prepared hybrid film, by immersing in a hydrochloric acid solution. The photoelectrochemical measurements and J–V characterisation of the hybrid film show an approximately fourfold increase in photocurrent density generation (114.22 µA/cm²), and approximately 25% enhancement of DSSC conversion efficiency (4.63%), compared to the acid-treated P25 paste alone (3.68%).     

Porous hydroxyapatite coating on strong ceramic substrate fabricated by low density slip coating-deposition and coating-substrate co-sintering

This study aims at developing a process technique, which can deposit porous scaffold-like hydroxyapatite (HA) coatings on strong ceramic substrates. As a first trial, micro-porous HA coatings on strong zirconia-based substrates are fabricated by the following technique—consisting of low-density HA-slip coating-deposition on the micro-porous substrates pre-sintered at 900 °C, and coating-substrate co-sintering at 1300 °C. The final co-sintering process ensures a strong bonding between the HA coating and the zirconia-based substrate after minimizing the mismatch in thermal expansion coefficients by adding alumina in HA coating and HA in zirconia-based substrate. The presence of porosity in the HA coating also reduces the mismatch. HA decomposition during the co-sintering process is discussed.