Synthesis and characterization of TiO<Subscript>2</Subscript>–NiO and TiO<Subscript>2</Subscript>–WO<Subscript>3</Subscript> nanocomposites

TiO₂–NiO and TiO₂–WO₃ nanocomposites were prepared by hydrothermal and surface modification methods. The samples were analyzed using X-ray diffraction, Scanning Electron Microscope images, Transmission Electron Microscope, Energy dispersive analysis, Zeta potential, Electrophoretic mobility and Photocatalysis activity measurement. XRD data sets of TiO₂–NiO, TiO₂–WO₃ powder nanocomposite have been studied for the inclusion of NiO, WO₃ on the anatase-rutile mixture phase of TiO₂ by Rietveld refinement. The cell parameters, phase fraction, the average grain size, strain and bond lengths between atoms of individual phases have been reported in the present work. Shifted positional co-ordinates of individual atoms in each phase have also been observed.     

Development and bio-electrochemical characterization of a novel TiO<Subscript>2</Subscript>–SiO<Subscript>2</Subscript> mixed oxide coating for titanium implants

Titanium and its alloys, the most commonly used materials for dental and orthopaedic implants are generally coated with bioactive materials such as sol-gel derived titania, silica and calcium phosphate in order to render these materials bioactive. In the present work a coating containing nanosized titania particles having anatase structure was developed on titanium substrate by thermal decomposition of titanium tetrachloride in isopropanol. A modified titania-silica mixed oxide coating was developed by incorporating the required amount of silica in the coating system. The presence of silica at small weight percentage caused improvement of adhesion and corrosion resistance of the coating. In vitro bioactivity tests were performed in 1.5 Kokubo's simulated body fluid after alkaline treatment of the titania/titania-silica coatings and the performance was compared with that of the titania coating developed by simple thermal oxidation. TF-XRD, FTIR and SEM-EDAX were used to investigate the microstructural morphology and crystallinity of the coatings. Elemental analysis of simulated body fluid was carried out using ICP-AES and spectrophotometry. Enhanced biogrowth was facilitated on the titania coating incorporated with low silica content.     

Synthesis of Y<Subscript>3</Subscript>Al<Subscript>5</Subscript>O<Subscript>12</Subscript>:Ce<Superscript>3+</Superscript> phosphor in the Y<Subscript>2</Subscript>O<Subscript>3</Subscript>–Al metal–CeO<Subscript>2</Subscript> ternary system

Garnet phosphor Y₃Al₅O₁₂:Ce³⁺ is prepared in the Y₂O₃–Al metal–CeO₂ ternary system by the solid-state reaction method in the air. For the first time, metal Al is used as a source of aluminum for the reaction instead of traditional oxide Al₂O₃. It is shown that the chemical reaction can be realized at lower temperatures and without use of special reducing atmosphere. The structural and spectroscopic properties of the prepared powder phosphor are very close to those earlier reported for the Y₃Al₅O₁₂:Ce³⁺ single crystal.     

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.     

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.     

The influence of high-temperature sintering on microstructure and mechanical properties of free-standing APS CeO<Subscript>2</Subscript>–Y<Subscript>2</Subscript>O<Subscript>3</Subscript>–ZrO<Subscript>2</Subscript> coatings

In this study, ceria–yttria co-stabilized zirconia (CYSZ) free-standing coatings, deposited by air plasma spraying (APS), were isothermally annealed at 1315 °C in order to explore the effect of sintering on the microstructure and the mechanical properties (i.e., hardness and Young’s modulus). To this aim, coating microstructure, before and after heat treatment, was analyzed using scanning electron microscopy, and image analysis was carried out in order to estimate porosity fraction. Moreover, Vickers microindentation and depth-sensing nanoindentation tests were performed in order to study the evolution of hardness and Young’s modulus as a function of annealing time. The results showed that thermal aging of CYSZ coatings leads to noticeable microstructural modifications. Indeed, the healing of finer pores, interlamellar, and intralamellar microcracks was observed. In particular, the porosity fraction decreased from ~10 to ~5% after 50 h at 1315 °C. However, the X-ray diffraction analyses revealed that high phase stability was achieved, as no phase decomposition occurred after thermal aging. In turn, both the hardness and Young’s modulus increased, in particular, the increase in stiffness (with respect to “as produced” samples) was equal to ~25%, whereas the hardness increased to up to ~60%.     

Spectroscopic characterisation of local structure in Y<Subscript>2</Subscript>O<Subscript>3</Subscript>–B<Subscript>2</Subscript>O<Subscript>3</Subscript>–Bi<Subscript>2</Subscript>O<Subscript>3</Subscript> glasses doped with gadolinium

Gadolinium doped bismuth borate glasses containing up to 30 mol% Y₂O₃ were prepared by fast melt quenching method. The effect of yttrium on the local order in 3B₂O₃ · Bi₂O₃ and B₂O₃ · Bi₂O₃ glass matrices, particularly on the bismuth sites, was investigated by infrared (IR) spectroscopy and electron paramagnetic resonance (EPR) of Gd³⁺ ions. The IR results show that the local structure is more ordered in the glass system with higher bismuth content and the progressive addition of yttrium increases the local disorder in both bismuth–borate glass matrices. The EPR results indicate that Gd³⁺ ions occupy both bismuth and yttrium sites and reflect the same structural disorder like that suggested by IR results.     

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.     

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.     

Phase Formation in Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–ZrO<Subscript>2</Subscript>–CeO<Subscript>2</Subscript> Nanopowders Modified with Calcium Cations

We have studied phase formation in calcium-modified Al₂O₃–ZrO₂–CeO₂ nanopowders during sol–gel synthesis. The results demonstrate that heat treatment of the nanopowders first leads to the formation of a zirconium dioxide-based solid solution stabilized with cerium cations. Raising the heat treatment temperature helps the crystallization of corundum, a stable phase of aluminum oxide, to reach completion. In the temperature range 1400–1550°C, we observe the formation of a second aluminum-containing phase: calcium cerium hexaaluminate consisting of long prismatic grains.     

Glasses formation,characterization, and crystal-structure determination in the Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>–Sb<Subscript>2</Subscript>O<Subscript>3</Subscript>–TeO<Subscript>2</Subscript> system prepared in an air

A glass-forming domain is found and studied within Bi₂O₃–Sb₂O₃–TeO₂ system. The glasses composition were obtained in pseudo-binary xSbO_1.5, (1−x)TeO₂ for 0.05 ≤ x ≤ 0.20. The constitution of glasses in the system Sb₂O₃–TeO₂ was investigated by DSC, Raman, and Infrared spectroscopy. The influence of a gradual addition of the modifier oxides on the coordination geometry of tellurium atoms has been elucidated based Infrared and Raman studies and showed the transition of TeO₄, TeO₃₊₁, and TeO₃ units with increasing Sb₂O₃ content. XRD results reveal the presence of three crystalline: γ-TeO₂, α-TeO₂, and SbTe₃O₈ phases during the crystallization process. The density of glasses has been measured. The investigation in the ternary system by the solid state reaction using XRD reveals the existence of a solid solution Bi_1−x Sb_1−x Te_2x O₄ isotopic to BiSbO₄ with 0 ≤ x ≤ 0.1.     

Investigation of solid solution of ZrP<Subscript>2</Subscript>O<Subscript>7</Subscript>–Sr<Subscript>2</Subscript>P<Subscript>2</Subscript>O<Subscript>7</Subscript>

In this study, ZrP₂O₇ was synthesized by the solid state reaction of ZrO₂ and NH₄H₂PO₄ at 900 °C. Then, in set 1; 10, 5, 1, 0.5, 0.1, 0.05, 0.03% previously prepared Sr₂P₂O₇ were doped into ZrP₂O₇, and Sr₂P₂O₇ slightly affect the unit cell parameter of cubic ZrP₂O₇ (a = 8.248(6)–8.233(8) Å). The reverse of this process was also applied to Sr₂P₂O₇ system (set 2). ZrP₂O₇ changes the unit cell parameters of orthorhombic Sr₂P₂O₇ in between a = 8.909(5)–8.877(5) Å, b = 13.163(3)–13.12(1) Å, and c = 5.403(2)–5.386(4) Å. Analysis of the vibrations of the P₂O ₇ ^4? ion and approximate band assignments for IR and Raman spectra are also reported in this work. Some coincidences in infrared and Raman spectra both sets were found and strong P–O–P bands were observed. Surface morphology, EDX analysis, and thermoluminescence properties of both sets were given the first time in this paper.     

Synthesis and properties of nanocrystalline 90 wt % ZrO<Subscript>2</Subscript>〈Y<Subscript>2</Subscript>O<Subscript>3</Subscript>, CeO<Subscript>2</Subscript>〉-10 wt % Al<Subscript>2</Subscript>O<Subscript>3</Subscript> powder

Using hydrothermal treatment of coprecipitated hydroxides, we have prepared nanocrystalline ZrO₂-rich ZrO₂-Y₂O₃-CeO₂-Al₂O₃ powder. The effect of heat treatment on the properties of the powder has been studied in the temperature range 400–1300°C. The powder has been shown to have a metastable phase composition, which is attributable to structural and size factors and also to the fact that the ZrO₂ and Al₂O₃ crystallites inhibit the growth of each other. Sintering the powder under various conditions, we have obtained ceramics with fracture toughnesses from 6.4 to 16.8 MPa m^1/2.     

CeO<Subscript>2</Subscript> and Co<Subscript>3</Subscript>O<Subscript>4</Subscript>–CeO<Subscript>2</Subscript> nanoparticles: effect of the synthesis method on the structure and catalytic properties in COPrOx and methanation reactions

CeO₂ and Co₃O₄–CeO₂ nanoparticles were synthesized, thoroughly characterized, and evaluated in the COPrOx reaction. The CeO₂ nanoparticles were synthesized by the diffusion-controlled precipitation method with ethylene glycol. A notably higher yield was obtained when H₂O₂ was used in the synthesis procedure. For comparison, two commercial samples of CeO₂ nanoparticles (Nyacol^®)—one calcined and the other sintered—were also studied. Catalytic results of bare CeO₂ calcined at 500 °C showed a strong influence of the method of synthesis. Despite having similar BET area values, the CeO₂ synthesized without H₂O₂ was the most active sample. Co₃O₄–CeO₂ catalysts with three different Co/(Co + Ce) atomic ratios, 0.1, 0.3, and 0.5, were prepared by the wet impregnation of the CeO₂ nanoparticles. TEM and STEM observations showed that impregnation produced mixed oxides composed of small CeO₂ nanoparticles located both over the surface and inside the Co₃O₄ crystals. The mixed oxide catalysts prepared with a cobalt atomic ratio of 0.5 showed methane formation, which started at 200 °C due to the reaction between CO₂ and H₂. However, above 250 °C, the reaction between CO and H₂ became important, thus contributing to CO elimination with a small H₂ loss. As a result, CO could be totally eliminated in a wide temperature range, from 200 to 400 °C. The methanation reaction was favored by the reduction of the cobalt oxide, as suggested by the TPR experiments. This result is probably originated in Ce–Co interactions, related to the method of synthesis and the surface area of the mixed oxides obtained.     

High-temperature heat capacity of the oxide compounds in the Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>–V<Subscript>2</Subscript>O<Subscript>5</Subscript> system

The compounds BiVO₄, Bi₄V₂O₁₁, and Bi₁₂V₂O₂₃ have been prepared by solid-state synthesis using stoichiometric mixtures of Bi₂O₃ and V₂O₅. The effect of temperature on the heat capacity of the synthesized bismuth vanadates has been studied by differential scanning calorimetry in the range 350–950 K. The C _p (T) curves have extrema at 531.7 K for BiVO₄ and at 725.2 and 852.8 K for Bi₄V₂O₁₁, which are due to polymorphic transformations of these compounds.     

Sintering behavior and microwave dielectric properties of Y<Subscript>2</Subscript>O<Subscript>3</Subscript>–ZnO doped (Zr<Subscript>0.8</Subscript>Sn<Subscript>0.2</Subscript>)TiO<Subscript>4</Subscript> ceramics

(Zr_0.8Sn_0.2)TiO₄ (ZST) ceramics were fabricated via conventional solid-state reaction method. Sintering behavior, phase composition, microstructure and microwave dielectric properties of Y₂O₃–ZnO doped ZST ceramics were investigated. Only a single ZST phase was identified by X-ray diffraction patterns. The variation tendencies of dielectric constants as well as Q × f values were in accordance with the bulk densities. The appropriate Y₂O₃ and ZnO additions could not only efficiently lower the sintering temperature to 1240 °C, but also noticeably improve the densification and microwave dielectric properties of ZST ceramics. But excessive additives deteriorated the microstructures and comprehensive properties of samples. A dielectric constant ε _r of 39.73, a Q × f value of 48,545 GHz (at 5.5 GHz), and a τ _f value of ?2.13 ppm/°C were obtained for 1 wt% ZnO doped ZST ceramics with 0.5 wt% Y₂O₃ addition sintered at 1240 °C.     

High-damping and high-rigidity composites of Al<Subscript>2</Subscript>TiO<Subscript>5</Subscript>–MgTi<Subscript>2</Subscript>O<Subscript>5</Subscript> ceramics and acrylic resin

High-damping materials are widely used in engineering fields. In order to increase the precision of vibration control to different levels, high-damping materials with high-rigidity are required. This study attempts to develop a new high-damping high-rigidity material using ductile ceramics based on the Al₂TiO₅–MgTi₂O₅ system, which has many continuous microcracks along the grain boundaries. Ductile ceramics have high internal friction (Q ⁻¹ = 0.01–0.037), but very low rigidity (<10 GPa). The rigidity of Al₂TiO₅–MgTi₂O₅ ceramics was improved by combining them with a polymer such as acrylic resin. The Young’s modulus and internal friction of the composites of Al₂TiO₅–MgTi₂O₅ ceramics and acrylic resin are investigated. They show high-damping capacity (Q ⁻¹ = 0.03–0.04) with high rigidity (E = 50–60 GPa), and their properties depend on those of the polymer. Thus, the composites fabricated using the above method can serve as high-damping high-rigidity materials.     

Preparation,structure and microwave dielectric properties of 3MgO–Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–3TiO<Subscript>2</Subscript> ceramics

3MgO–Al₂O₃–3TiO₂ (MAT) ceramics were prepared by a conventional solid-state reaction method. The crystal structure, sintering behavior and microwave dielectric properties of ceramics were investigated using X-ray diffraction, scanning electron microscopy and network analyzer. MAT ceramics contained the coexistence of three phases, including MgAl₂O₄, MgTiO₃ and MgTi₂O₅. The ceramics sintered at 1350 °C for 4 h presented excellent comprehensive performances with relative permittivity (ε _r ) of 15.4, quality factor (Q × f) of 91,000 GHz and temperature coefficient of resonant frequency (τ _f ) about ?55.1 ppm/°C.     

Frequency dependence of dielectric properties of CaO–SrO–Li<Subscript>2</Subscript>O–Ln<Subscript>2</Subscript>O<Subscript>3</Subscript>–TiO<Subscript>2</Subscript> ceramics

CaO–SrO–Li₂O–Ln₂O₃–TiO₂ ceramics were prepared by solid state reaction method, where Ln₂O₃ consists of equal proportions of Nd₂O₃ and Sm₂O₃. Dielectric properties and crystal structure were investigated with respect to the content of TiO₂. Single phase with an orthorhombic perovskites structure was formed within the composition range of investigation. The frequency dependence of dielectric properties of the present ceramics was extensively investigated. Dielectric constant was less sensitive to frequency. However, dielectric loss and temperature coefficients were both very sensitive to frequency and gradually decreased with increasing frequency, such as the variation was more than ten times between 1 MHz and several GHz. The relationship between the temperature coefficient and dielectric loss was also discussed at different frequencies. And the mechanism of the frequency dependence was discussed in term of the role of Li ions.     

A sol–gel-derived α-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> crystal interlayer modified 316L porous stainless steel to support TiO<Subscript>2</Subscript>, SiO<Subscript>2</Subscript>, and TiO<Subscript>2</Subscript>–SiO<Subscript>2</Subscript> hybrid membranes

A homogeneous α-Al₂O₃ crystal membrane was fabricated by the sol–gel technique on 316L porous stainless steel (PSS) substrate with an average pore size of 1.0 μm. The preparation process was optimized by carefully choosing the binder, the concentrations of the casting solutions and the sintering temperatures of the membranes. Compared to methylcellulose and polyethylene glycol 20000, polyvinyl alcohol 1750 was found to be the most effective binder to fabricate a homogeneously structured Al₂O₃ membrane without defects. The concentration to prepare an uniform coverage membrane with a thickness of ~10 μm was 0.032 mol/L. When sintered at 1000 °C, γ-Al₂O₃ membrane with ~3 μm grains was obtained. When sintered at 1200 °C, γ-Al₂O₃ completely transformed into α-Al₂O₃ and the grains grew to ~5 μm. Accordingly, the process was applied to a bigger pore-sized PSS with an average pore size of 1.5 μm to fabricate an α-Al₂O₃ intermediate layer to initially modify its surface. A single α-Al₂O₃ crystal layer with a thickness of ~5 μm and an average pore size of 0.7 μm was achieved. Subsequently, TiO₂, SiO₂, and TiO₂–SiO₂ hybrid membranes were tried on the modified PSS. Defect-free microfiltration membranes with average pore sizes of ~0.3 μm were readily fabricated. The results indicate that the sol–gel method is promising to initially modify the PSS substrates and the sol–gel-derived α-Al₂O₃ crystal layer is an appropriate intermediate layer to modify the PSS and to support smaller grain-sized top membranes.