New insights in photo-patterned sol–gel-derived TiO<Subscript>2</Subscript> films

Specific sol–gel formulations and protocols have been adapted to the fine patterning of TiO₂ films using a very simplified UVA three-step lithography method. Mechanisms occurring during the photo-patterning procedure and a post-patterning thermal treatment have been studied by Fourier transform infrared spectroscopy, atomic force microscopy, X-ray diffraction, and ellipsometry. Discussions are proposed to support the influence of the photo-patterning procedure and post-patterning treatment on the shape and the dimension of so-formed microstructures. Original additional functionalities arising from such structures are also presented.     

Crystallization and microstructural evolution of MgO–Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–SiO<Subscript>2</Subscript>–TiO<Subscript>2</Subscript>–La<Subscript>2</Subscript>O<Subscript>3</Subscript> glass-ceramics

Crystallization and microstructure of glasses with the molar compositions 1MgO·1.2Al₂O₃·2.8SiO₂·1.2TiO₂·xLa₂O₃ (x = 0.1 and 0.4) were thermally treated at different temperatures in the range from 950 to 1250 °C and then analyzed by X-ray diffraction and scanning electron microscopy, in combination with energy-dispersive X-ray spectroscopy and electron backscatter diffraction. It was found that the microstructure is first homogeneous with the precipitation of randomly distributed crystals and then indialite domains with embedded perrierite and rutile crystals are formed. For higher temperatures or prolonged times, more domains appear and expand into the bulk of the sample. Finally, the entire sample consists of the indialite domains and the boundaries that are enriched in rutile, perrierite, and magnesium aluminotitanate. Nevertheless, very distinct differences are observed between the samples with different La₂O₃ concentrations. For the sample with x = 0.4, the domains were detected at lower temperatures, while the quantity and size of the domains increase faster due to the promoted precipitation of indialite. For the sample with x = 0.1, in addition to the domain boundaries, secondary boundaries between the “regions” (assemblages of the domains) are observed in a larger length scale. The average size of the crystalline phases found between the “regions” is larger than that typically observed at the domain boundaries. The sizes of the crystals at the boundaries decrease with higher concentrations of La₂O₃, and the crystals (especially perrierite) within the domains become larger, resulting in a more homogeneous microstructure. This results in better dielectric properties, i.e., much higher quality factor for the sample with x = 0.4 in comparison to that with x = 0.1 after heat-treatment at 1150 or 1250 °C.     

Synthesis and thermoanalytical study of SiO<Subscript>2</Subscript>–TiO<Subscript>2</Subscript> composites modified with macrocyclic endoreceptors

We have developed processes for the fabrication of SiO₂–TiO₂ composites containing crown ethers (CEs) with composite: CE weight ratios from 1: 0.06 to 1: 1. As oxide sources, we used titania and silica sols. The composites were characterized by differential thermal analysis, X-ray diffraction, and adsorption gravimetry. The results demonstrate that most of the water and the solvent are bound into a complex with the CE, which decomposes at temperatures from 170 to 230°C. The temperature range of CE removal depends on the SiO₂: TiO₂ and oxide: CE ratios in the composite. Our results demonstrate effectiveness of strontium cation imprint formation in an adsorbent in the sol–gel processing step, which ensures an increase in the amount of strontium cation adsorption by 20%. We have identified conditions for quantitative lanthanum, strontium, and barium adsorption on the synthesized composites.     

Syntheses and proton conductivity of mesoporous Nd<Subscript>2</Subscript>O<Subscript>3</Subscript>–SiO<Subscript>2</Subscript> and NdOCl–SiO<Subscript>2</Subscript> composites

Two mesoporous oxide composites of Nd₂O₃–SiO₂ and NdOCl–SiO₂ were synthesized using SBA-15 as a template and neodymium nitrate or neodymium chloride as a precursor. The porous Nd₂O₃–SiO₂ with a SBA-15-like structure has amorphous walls and the porous NdOCl–SiO₂ with a replicated structure of SBA-15 has crystalline walls. These porous materials were characterized by X-ray diffraction, transmission electron microscopy and nitrogen adsorption/desorption. They exhibited significant proton conductivities in the presence of moisture at low temperatures and the highest conductivity observed was 4.55 × 10⁻⁴ S/cm at 47 °C in wet air (RH = 28.6%).     

Catalytic activity of CuO-loaded TiO<Subscript>2</Subscript>/γ-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> for NO Reduction by CO

The activities in NO + CO reaction of CuO-loaded TiO₂/γ-Al₂O₃ catalysts prepared by precipitation (P), co-precipitation (C-P), or sol-gel (S-G) were examined using a micro-reactor-gas chromatography (GC) system. The study showed higher catalytic activity of 12%CuO/15%TiO₂/γ-Al₂O₃ (P) than that of 12%CuO/15%TiO₂/γ-Al₂O₃ (S-G) or 12%CuO/15%TiO₂/γ-Al₂O₃ (C-P) in air condition, compared with higher activity of 12%CuO/15%TiO₂/γ-Al₂O₃ (P) or 12%CuO/15%TiO₂/γ-Al₂O₃ (S-G) than that of 12%CuO/15%TiO₂/γ-Al₂O₃ (C-P) in H₂ condition. The specific surface area and crystallite formation had little effect on catalytic activities. H₂-temperature programmed reduction (TPR) revealed four reduction peaks of 12%CuO/15%TiO₂/γ-Al₂O₃ (P), three reduction peaks of 12%CuO/15%TiO₂/γ-Al₂O₃ (S-G), but only one reduction peak of 12%CuO/15%TiO₂/γ-Al₂O₃ (C-P). CuO diffraction peaks were detected only in 12%CuO/15%TiO₂/γ-Al₂O₃ (P), indicating that CuO was highly dispersed on the other two TiO₂/γ-Al₂O₃ catalysts. As a result, 12%CuO/15%TiO₂/γ-Al₂O₃ (P) had the highest activity of reducing NO. During NO + CO reaction, the absorption peaks of intermediate product N₂O were shown at 150 °C by 12%CuO/15%TiO₂/γ-Al₂O₃ (P), at 200 °C by 12%CuO/15%TiO₂/γ-Al₂O₃ (S-G), and at 100 °C by 12%CuO/15%TiO₂/γ-Al₂O₃ (C-P) after H₂ pretreatment at 400 °C for 1 h.     

Optically stimulated luminescence of proton-irradiated α-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> crystals

We present the results of the first domestic experimental investigation of the optically stimulated luminescence (OSL) in commercial thermoluminescence (TL) detectors based on proton-irradiated anion-defect corundum. It is demonstrated that the OSL and TL phenomena can, in principle, be jointly used for the dose diagnostics of accelerated particle beams. The observed phenomena have good prospects for application in radiation physics.     

Evaluation of CaO–SiO<Subscript>2</Subscript>–P<Subscript>2</Subscript>O<Subscript>5</Subscript>–Na<Subscript>2</Subscript>O–Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> bioglass-ceramics for hyperthermia application

Magnetic bioglass ceramics (MBC) are being considered for use as thermoseeds in hyperthermia treatment of cancer. While the bioactivity in MBCs is attributed to the formation of the bone minerals such as crystalline apatite, wollastonite, etc. in a physiological environment, the magnetic property arises from the magnetite [Fe₃O₄] present in these implant materials. A new set of bioglasses with compositions 41CaO · (52 ? x)SiO₂ · 4P₂O₅  · xFe₂O₃ · 3Na₂O (2 ≤ x ≤ 10 mol% Fe₂O₃) have been prepared by melt quenching method. The as-quenched glasses were then heat treated at 1050°C for 3 h to obtain the glass-ceramics. The structure and microstructure of the samples were characterized using X-ray diffraction and microscopy techniques. X-ray diffraction data revealed the presence of magnetite in the heat treated samples with x ≥ 2 mol% Fe₂O₃. Room temperature magnetic property of the heat treated samples was investigated using a Vibrating Sample Magnetometer. Field scans up to 20 kOe revealed that the glass ceramic samples had a high saturation magnetization and low coercivity. Room temperature hysteresis cycles were also recorded at 500 Oe to ascertain the magnetic properties at clinically amenable field strengths. The area under the magnetic hysteresis loop is a measure of the heat generated by the MBC. The coercivity of the samples is another important factor for hyperthermia applications. The area under the loop increases with an increase in Fe₂O₃ molar concentration and the. coercivity decreases with an increase in Fe₂O₃ molar concentration The evolution of magnetic properties in these MBCs as a function of Fe₂O₃ molar concentration is discussed and correlated with the amount of magnetite present in them.     

In vitro dissolution behavior of SiO<Subscript>2</Subscript>–MgO–Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–K<Subscript>2</Subscript>O–B<Subscript>2</Subscript>O<Subscript>3</Subscript>–F glass–ceramic system

Herein, we report the results of the in vitro dissolution tests, which were carried out by immersing the selected glass-ceramic samples in artificial saliva (AS) for various time periods of up to 42 days. In our experiments, the SiO(2)-MgO-Al(2)O(3)-K(2)O-B(2)O(3)-F glass ceramics with different crystal morphology and crystal content were used and a comparison is also made with the baseline glass samples (without any crystals). The bioactivity of the samples was probed by measuring the changes in pH, ionic conductivity and ionic concentration of AS following in vitro dissolution experiments. High resistance of the selected glass-ceramic samples against in vitro leaching has been demonstrated by minimal weight loss (<1%) and insignificant density change, even after 6 weeks of dissolution in artificial saliva. While XRD analysis reveals the change in surface texture of the crystalline phase, FT-IR analysis weakly indicated the Ca-P compound formation on the leached surface. The experimental measurements further indicate that the leaching of F(-), Mg(2+) ions from the sample surface commonly causes the change in the surface chemistry. Furthermore, the presence of (Ca, P, O)-rich mineralized deposits on the leached glass-ceramic surface as well as the decrease in Ca(2+) ion concentrations in the leaching solutions (compared to that in the initial AS solution) provide evidences of the moderate bioactive or mild biomineralisation behaviour of investigated glass-ceramics.     

Influence of Bi substitution on microwave dielectric properties of BaO–La<Subscript>2</Subscript>O<Subscript>3</Subscript>–Sm<Subscript>2</Subscript>O<Subscript>3</Subscript>–TiO<Subscript>2</Subscript> ceramics

The influences of Bi substitution on microwave dielectric properties of Ba₄(La_0.5Sm_0.5)_9.33Ti₁₈O₅₄ solid solutions were investigated. Dielectric ceramics with general formula Ba₄(La_(0.5−z)Sm_0.5Bi _z )_9.33Ti₁₈O₅₄, z = 0.0–0.2 were prepared by conventional solid state route. The structural analysis of all the samples was carried out by X-ray diffraction and scanning electron microscopy. The dielectric properties were investigated as a function of Bi contents using open-ended coaxial probe method in the frequency range 0.3–3.0 GHz at room temperature. Dielectric constant varies from 83 to 88 and loss tangent from 2.1 × 10⁻³ to 5.5 × 10⁻³ at 3 GHz with temperature coefficient of resonant frequency changing from 106.7 to −8.4 ppm/oC as Bi contents increases from z = 0.00–0.20. It has been found that dielectric constant and temperature coefficient of resonant frequency improve whereas loss tangent is adversely affected with increase in Bi substitution.     

Hardness properties and microscopic investigation of crack–crystal interaction in SiO<Subscript>2</Subscript>–MgO–Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–K<Subscript>2</Subscript>O–B<Subscript>2</Subscript>O<Subscript>3</Subscript>–F glass ceramic system

In view of the potential engineering applications requiring machinability and wear resistance, the present work focuses to evaluate hardness property and to understand the damage behavior of some selected glass–ceramics having different crystal morphologies with SiO₂–MgO–Al₂O₃–K₂O–B₂O₃–F composition, using static micro-indentation tests as well as dynamic scratch tests, respectively. Vickers hardness of up to 5.5 GPa has been measured in glass–ceramics containing plate like mica crystals. Scratch tests at a high load of 50 N in artificial saliva were carried out in order to simulate the crack–microstructure interaction during real-time abrasion wear and machining operation. The experimental observations indicate that the novel “spherulitic-dendritic” shaped crystals, similar to the plate like crystals, have the potential to hinder the scratching induced crack propagation. In particular, such potential of the ‘spherulitic-dendritic’ crystals become more effective due to the larger interfacial area with the glass matrix as well as the dendritic structure of each mica plate, which helps in crack deflection and crack blunting, to a larger extent. While modest damage tolerant behavior is observed in case of ‘spherulitic-dendritic’ crystal containing material, severe brittle fracture of plate like crystals were noted, when both were scratched at 50 N load.     

Phytic acid derived bioactive CaO–P<Subscript>2</Subscript>O<Subscript>5</Subscript>–SiO<Subscript>2</Subscript> gel-glasses

The possibility of using phytic acid as a precursor to synthesize CaO–P₂O₅–SiO₂ glasses by sol–gel method has been explored and the pseudo ternary phase diagram has been established. It was shown that gel-glasses over a broader range of compositions could be prepared compared to other phosphorus precursors or melt-quenching method. Furthermore, phytic acid was found to assist calcium being incorporated into glass networks. In vitro tests in simulated body fluid (SBF) were performed on the above gel–glasses and it was found that they were bioactive over a much broader compositional range especially at high phosphate content, thus enabling one to design bioactive materials with various degradation rates by adjusting the phosphate content.     

Reaction of CaAl<Subscript>4</Subscript>O<Subscript>7</Subscript> with (0001)-oriented α-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>

Reactions between thin films of CA₂ and (0001)-oriented α-Al₂O₃ have been studied using a combination of microscopy techniques. Thin films of amorphous CA₂ were deposited on sapphire substrates by pulsed-laser deposition at 900 °C in an oxygen ambient atmosphere. After deposition, the reaction couples were heat treated in air for various times either at 1300 or 1400 °C. Atomic-force microscopy was used to monitor changes in the microstructure of the films. Interfaces between the different regions were examined by transmission electron microscopy (TEM) of cross-sectional samples prepared by focused ion-beam milling. The CA₂ films had dewetted the substrate surface as a result of the heat treatment. An interfacial reaction layer was observed between the dewetted CA₂ droplets and the substrate. The structure of this reaction layer was found to be consistent with γ-Al₂O₃ by computer analysis of high-resolution TEM images. There is a perfect epitaxy between the interfacial layer and the substrate. For the samples heat treated for longer times, hexagonal features were found on the substrate surface. The presence of these features on (0001)-oriented α-Al₂O₃ suggests that CA₆ platelets form by the transformation of the interfacial reaction layer. The results are discussed in relation to the crystallization behavior of the various calcium aluminate phases and the equilibrium-phase diagram of the CaO–Al₂O₃ system.     

Fabrication of Yb<Subscript>2</Subscript>O<Subscript>3</Subscript>–Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–P<Subscript>2</Subscript>O<Subscript>5</Subscript>–SiO<Subscript>2</Subscript> Optical Fibers with a Perfect Step-Index Profile by the MCVD Process

An all-vapor phase MCVD process has been proposed for the fabrication of fiber preforms with a Yb₂O₃–Al₂O₃–P₂O₅–SiO₂ multicomponent glass core. We have investigated the tubular preform collapse into a rod and demonstrated approaches capable of preventing P₂O₅ losses in the central part of the core during the collapse process. Preforms with a flat, perfect step-index profile have been fabricated.     

Free-standing TiO<Subscript>2</Subscript>–SiO<Subscript>2</Subscript>/PANI composite nanofibers for ammonia sensors

Free-standing TiO₂–SiO₂/polyaniline (TS/PANI) composite nanofibers were prepared by electrospinning, in situ polymerization and calcination method. The effect of tetra-n-butyl titanate (TBT) in the electrospinning solution on the morphology and the ammonia sensing properties of TS/PANI composite nanofibers were investigated. The obtained nanofibers were characterized by scanning electron microscope, Fourier transform infrared spectroscopy, X-ray diffraction, transmission electron microscopy, thermo-gravimetric analysis and gas sensor test system. It is proved that too much TBT in the solution would make the fibrous morphology and ammonia sensing properties worse. Gas sensing tests showed that the TS/PANI composite nanofibers ammonia sensor can work at room temperature and possess ideal response values, selectivity and repeatability. With the increase in TiO₂ content in the TS nanofibers, the ammonia sensing properties were improved because of the increase in P–N heterojunctions formed between TiO₂ and PANI in the sensors.     

Structure–property correlations in the SiO<Subscript>2</Subscript>–PbO–Bi<Subscript>2</Subscript>O<Subscript>3</Subscript> glasses

SiO₂–PbO–Bi₂O₃ glasses having the composition of 35SiO₂–xPbO–(65−x)Bi₂O₃ (where x = 5, 10, 15, 20, 25, 35, 45; in mol%) have been prepared using the conventional melting and annealing method. Density, molar volume and Vickers microhardness of the prepared glasses were measured. Infrared (IR) and UV–visible spectroscopic techniques were used for structural studies of these glasses. Density as well as the microhardness increase systematically and, conversely, the molar volume decreases with increasing the lead oxide content. This behavior can be explained by the correlation with the glass structure. Increasing the lead oxide content (≥20 mol%) increases the network former PbO₄ groups which can play an important role in increasing the connectivity and compactness of the glass matrix via increasing the cross-linking with the other constituent silicate and bismuthate structural units. The increased compactness may explain, in turn, the increase of the density and microhardness. IR spectra reinforce the idea that bismuth participates in the glassy network predominantly as BiO₆ octahedral structural units. UV–VIS optical absorption spectra revealed UV-charge transfer absorption bands related to the contribution of Pb²⁺ ions in the region 350–385 nm; in addition to the extrinsic absorption of trace iron impurities in the range 220–290 nm. In the visible region, three optical bands in the ranges 415–435, 605–650 and 880–890 nm were correlated with the contribution of electronic transitions in Bi³⁺ ions. Calculation of the optical mobility gap and the width of the energy tail of glass from the UV–VIS absorption indicated a slight increase followed by a decrease in their values. The behavior change occurred at the glass in which PbO content is 20 mol% where lead oxide starts to participate into the glassy matrix as a network former. The combination of analytical FTIR and UV–visible spectroscopy provided a consistent picture of structure–property relations in this glass system.     

Catalytic combustion of methane over Pt and PdO-supported CeO<Subscript>2</Subscript>–ZrO<Subscript>2</Subscript>–Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>/γ-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalysts

Catalytic combustion of methane was investigated on Pt and PdO-supported CeO₂–ZrO₂–Bi₂O₃/γ-Al₂O₃ catalysts prepared by a wet impregnation method in the presence of polyvinylpyrrolidone. The catalysts were characterized by X-ray fluorescence analysis, X-ray powder diffraction, X-ray photoelectron spectra, transmission electron microscopy, and BET specific surface area measurements. The Pt/CeO₂–ZrO₂–Bi₂O₃/γ-Al₂O₃ and PdO/CeO₂–ZrO₂–Bi₂O₃/γ-Al₂O₃ catalysts were selective for the total oxidation of methane into carbon dioxide and steam, and no by-products such as HCHO, CO, and H₂ were obtained. The catalytic activities of the PdO/CeO₂–ZrO₂–Bi₂O₃/γ-Al₂O₃ catalysts were relatively higher than those of the Pt-supported catalysts, due to the facile re-oxidation of metallic Pd into PdO based on lattice oxygen supplied from the CeO₂–ZrO₂–Bi₂O₃ bulk. A decrease in the calcination temperature during the preparation process was found to be effective in enhancing the specific surface area of the catalysts, whereby particle agglomeration was inhibited. Optimization of the PdO amount and calcination temperature enabled complete oxidation of methane at temperatures as low as 320 °C on the 11.6 wt% PdO/CeO₂–ZrO₂–Bi₂O₃/γ-Al₂O₃ catalyst prepared at 400 °C.     

Preparation and characterization of Li<Subscript>2</Subscript>O–CaO–Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–P<Subscript>2</Subscript>O<Subscript>5</Subscript>–SiO<Subscript>2</Subscript> glasses as bioactive material

The aim of the present investigation was to study the role of Al₂O₃ in the Li₂O–CaO–P₂O₅–SiO₂ bioactive glass for improving the bioactivity and other physico-mechanical properties of glass. A comparative study on structural and physico-mechanical properties and bioactivity of glasses were reported. The structural properties of glasses were investigated by X-ray diffraction, Fourier transform infrared spectrometry, scanning electron microscopy and the bioactivity of the glasses was evaluated by in vitro test in simulated body fluid (SBF). Density, compressive strength, Vickers hardness and ultrasonic wave velocity of glass samples were measured to investigate physical and mechanical properties. Results indicated that partial molar replacement of Li₂O by Al₂O₃ resulted in a significant increase in mechanical properties of glasses. In vitro studies of samples in SBF had shown that the pH of the solution increased after immersion of samples during the initial stage and then after reaching maxima it decreased with the increase in the immersion time. In vitro test in SBF indicated that the addition of Al₂O₃ up to 1.5 mol% resulted in an increase in bioactivity where as further addition of Al₂O₃ caused a decrease in bioactivity of the samples. The biocompatibility of these bioactive glass samples was studied using human osteoblast (MG-63) cell lines. The results obtained suggested that Li₂O–CaO–Al₂O₃–P₂O₅–SiO₂-based bioactive glasses containing alumina would be potential materials for biomedical applications.     

Comparative study of multilayered ZnO/TiO<Subscript>2</Subscript>/ZnO and TiO<Subscript>2</Subscript>/ZnO/TiO<Subscript>2</Subscript> thin films prepared by sol–gel dip coating method

The aim of this research work is to represent the comparative study of ZnO/TiO₂/ZnO (ZTZ) and TiO₂/ZnO/TiO₂ (TZT) thin films deposited by sol–gel dip coating on FTO substrates. After deposition, the films were annealed at 500 °C for 1 h. Structural, surface morphology, optical and electrical properties of these films were studied by X-ray diffractrometer (XRD), Raman spectra, atomic force microscope (AFM), photoluminescence spectra (PL) and four point probe technique respectively. XRD and Raman spectra confirmed the anatase, brookite phases of TiO₂ and cubic phase of ZnO. AFM confirmed the formation of nano particles with average sizes of 18.4 and 47.2 nm of TZT and ZTZ films respectively. According to PL spectra, both the multilayer films slowdown the electron hole recombination rate and enhances the optoelectronic properties of the materials. Also it showed the peaks in the visible region of spectrum. The four point probe results showed that the average sheet resistivity of the films is 450 and 120 (ohm-m) respectively.     

Characterization and analysis of CaO–SiO<Subscript>2</Subscript>–B<Subscript>2</Subscript>O<Subscript>3</Subscript> ternary system ceramics

The dielectric, thermal and mechanical properties of CaO–SiO₂–B₂O₃ ternary system ceramics by solid-phase method have been carried out and quantitive analysis been examined by X-ray diffraction (XRD) patterns. The results showed that the major crystalline phase of CaO–SiO₂–B₂O₃ ternary system ceramics was wollastonite (about 90 wt%) which existed at the temperature ranging from 950 to 1,100 °C. It is also observed that wollastonite could be transformed to pseudowollastonite at 1,200 °C. In addition, with increase in calcination temperature, the amount of wollastonite increases. When the sintering temperature is at 1,100 °C, the amount of wollastonite has a maximum value of 92.7 wt%. Accordingly, CaO–SiO₂–B₂O₃ ternary system ceramics achieved excellent properties at 1,100 °C, such as dielectric constant of 8.38, dielectric loss of 1.51 × 10⁻³ at 1 MHz, linear thermal-expansion coefficient (300 K) of 6.68 × 10⁻⁶/K, bending strength of 121.75 Mpa. Analysis of the mechanical and dielectric properties showed that the measured bending strength, dielectric constant and loss of CaO–SiO₂–B₂O₃ ternary system ceramics can be substantially modified and improved by controlling the sintering temperature, in particular due to the amount of wollastonite crystalline phase and size of grains.