Effects of the geometry and operating temperature on the stability of Ti/IrO<Subscript>2</Subscript>–SnO<Subscript>2</Subscript>–Sb<Subscript>2</Subscript>O<Subscript>5</Subscript> electrodes for O<Subscript>2</Subscript> evolution

Ternary IrO₂–Sb₂O₅–SnO₂ anode has shown its superiorities over IrO₂ and many other electrocatalysts for O₂ evolution, in terms of electrochemical stability, activity and cost. The performance of IrO₂–Sb₂O₅–SnO₂ anodes is affected by its electrochemical properties and operating conditions. In this paper, the electrochemical stability and activity of the Ti/IrO₂–Sb₂O₅–SnO₂ anodes prepared with three different geometries were investigated under different operating conditions. It was found that anodes with large mean curvature have high electrochemical stability. Although increasing temperature results in a decrease in the stability of Ti/IrO₂–Sb₂O₅–SnO₂, the anode with a mean curvature of 200 m⁻¹ still shows acceptable service life even at 70 °C. This tolerance of high temperature was attributed to the thermal expansion difference between the substrate and the coating layer, the redox window for Ir(V)/Ir(IV) conversion, and the redox reversibility of Sb and Sn species in the coating layer.     

Electrochemical oxidation of sulfide ion at a Ti/IrO<Subscript>2</Subscript>–Ta<Subscript>2</Subscript>O<Subscript>5</Subscript> anode in the presence and absence of naphthenic acids

Electrochemical oxidation of sulfide ion at a Ti/IrO₂–Ta₂O₅ anode followed partial order kinetics (between current and mass transport control) in the absence and presence of chloride ion and of naphthenic acids, at sulfide concentrations typical of sour brines. The desired outcome was to promote the 2-electron oxidation of sulfide to elemental sulfide rather than the 8-electron oxidation to sulfate. Although elemental sulfur accumulated to some extent at low conversion of sulfide, sulfate ion became the principal product as the reaction progressed. At high conversion, the overall current efficiencies were typically higher than 50%, with material balance about 90%. However, this anode material was gradually poisoned by sulfide in long term use.     

Comparison of Ti/BDD and Ti/SnO<Subscript>2</Subscript>–Sb<Subscript>2</Subscript>O<Subscript>5</Subscript> electrodes for pollutant oxidation

Anodic oxidation is a promising process for degrading toxic and biologically refractory organic pollutants present in wastewater treatment. Proper selection of electrodes is the key to reach effective and economic operation. In this study, two types of electrodes, i.e. the recently developed Ti/BDD and Ti/SnO₂–Sb₂O₅, which is generally believed to be superior to the conventional electrodes, were compared under the same conditions. It was found that the Ti/BDD electrode could mineralize both phenol and reactive dyes effectively. But the Ti/SnO₂–Sb₂O₅ electrode could only mineralize phenol. When oxidizing more refractory reactive dyes, it demonstrated very poor activity. In addition, the Ti/BDD electrode had a service life of 264 h in an accelerated life test, but the Ti/SnO₂–Sb₂O₅ was irreversibly damaged within several seconds. The direct experimental comparison in the present study indicates that the Ti/BDD electrode is much better than the Ti/SnO₂–Sb₂O₅ electrode for pollutant oxidation.     

Formation and stability of glasses with ultra-optical properties in TiO<Subscript>2</Subscript>–Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>–PbO system

To obtain ultra-optical property in glasses, as the basis for photonic applications, the glass forming region of TiO₂–Bi₂O₃–PbO system was investigated and determined by melting series of compositions in the system. The glass-forming boundary region was defined. The best compositions for glass formation were found to be around the eutectic and peritectic regions in the corresponding phase diagram. Generally, stability increased with the addition of TiO₂, acting as a conditional glass former, to a maximum of 15TiO₂ mol %. Replacing PbO with Bi₂O₃ in the glass worsened the stability, due to the increase of heavy cation Bi^3– in the glass structure. Finally, the refractive index and dispersion of some stable glasses were measured, which were as high as 2.435 and 10.2, respectively.     

Structural heterogeneity of SiO<Subscript>2</Subscript>–Na<Subscript>2</Subscript>O–Al<Subscript>2</Subscript>O<Subscript>3</Subscript> glass

It is shown that the phase heterogeneity of SiO₂–Na₂O–Al₂O₃ glass has a liquation and crystallization nature, the balance between which is determined by the conditions of their synthesis. An increase in the aluminum oxide content decreases the number of liquation and crystallization sites, and also the linear sizes of the crystalline formations without eliminating the phase separation due to the liquation. The area of metastable immiscibility in the SiO₂–Na₂O–Al₂O₃ system, which is determined by scanning electron microscopy, is probably wider than the area detected by the optical methods.     

Effect of preparation procedure of Iro<Subscript>2</Subscript>–Nb<Subscript>2</Subscript>o<Subscript>5</Subscript> anodes on surface and electrocatalytic properties

The influence of the electrode manufacturing procedure on surface and electrocatalytic properties for oxygen and ozone evolution at electrodes of nominal composition Ti/[IrO₂–Nb₂O₅] (45:55 mol%) was investigated. Thermal decomposition at 450 °C (1 h, air stream) was adopted as standard procedure. Metal support pretreatment, solvent mixture, method of applying the precursor mixture and calcination procedure were all investigated. X-ray diffraction, scanning electronic microscopy, voltammetric and differential capacity analysis show the use of HCl 1:1 as solvent and applying the mixture by brush led to fragile rugged/porous oxide coatings. However, for the same conditions, but controlled calcination (heating/cooling rates), the coating becomes more compact. Using isopropanol as solvent results in a more homogeneous coating, presenting the lowest morphology factor. Kinetic investigation shows the rugged/porous coating presents the lowest Tafel slopes and the highest global electrocatalytic activity for OER. The more compact the coating the lower the electrochemically active surface area and the global OER activity. Ozone efficiency depends on the electrochemically active area while support pretreatment strongly influences the lifetime of the electrode. Application of a Pt interlayer between the oxide and Ti base improves the service life.     

Self-cleaning performance of sol–gel-derived TiO<Subscript>2</Subscript>/SiO<Subscript>2</Subscript> double-layer thin films

The self-cleaning properties of the TiO₂/SiO₂ double-layer films prepared by sol–gel method were investigated. Thin films were prepared by spin coating onto glass and then thermally treated at different temperatures, and characterized using X-ray diffraction, atomic force microscopy, field emission scanning electron microscopy, and UV–visible spectroscopy. The cross-sectional structure of the films was observed by FESEM. The surface roughness of the films was characterized by AFM. The root mean square surface roughness of the thin films was below 2 nm, which should enhance their optical transparency. The photo-induced hydrophilicity of the films was evaluated by water contact angle measurement in air. The photocatalytic activity of the films was studied by the photocatalytic degradation of methylene blue under UV light irradiations. The TiO₂/SiO₂ double-layer thin films are plausibly applicable to developing self-cleaning materials in various applications such as windows, solar panels, cement, and paints.     

Mechanical,Structural and Thermal Properties of Transparent Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>–Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–ZnO–TeO<Subscript>2</Subscript> Glass System

Oxide based optical glass materials has important potential material in many applications from fiber optic to sensor due to the high transparency and amourphous structures. The objective of this study is to synthesize the novel optical glass materials based on the bismuth and aluminum contents to be able to determine the physical, chemical and mechanical properties by considering the systematic experimental steps. In this study, Bi₂O₃–Al₂O₃ based tellurite optical glasses have been prepared by using conventional melt quenching method as a function of the both Bi₂O₃ and Al₂O₃ compositions. There is a strong interactions between the glass former and modifier ions that might effect on the structure and mechanical properties. During the experimental steps, thermal, structural and mechanical properties of the prepared glass materials have been determined considering the DTA/DSC, FT-IR spectroscopy, SEM and Vicker’s hardness techniques, respectively. Thermal parameters, like glass transition, T_g, onset, T_x, crystallization, T_p, and melting, T_m, temperatures were obtained by using DTA scan.     

Fine Ti Powders Through Metallothermic Reduction in TiO<Subscript>2</Subscript>–Mg–Ca Mixtures

Fine Ti powders were prepared through magnesiothermic reduction in TiO₂–Mg–Ca mixtures under 4 MPa of Ar followed by acid leaching (with HCl or HNO₃) and characterized by XRD, SEM/EDS, and chemical analysis. Thus prepared Ti powders exhibited the specific surface ranging between 7.0 and 30.0 m²/g. The produced Ti powders can find their application in pyrotechnics, powder metallurgy, and as raw material for SHS of inorganic compounds.     

Micro- and nanocomposite particles of the Cu–TiO<Subscript>2</Subscript> system

The micro- and nanocomposite particles of the Cu–TiO₂ system are synthesized using the laser scanning of a heliumlike film. A model of nanostructure formation on a dielectric surface is proposed.     

Migration processes in the glass forming melts of the Na<Subscript>2</Subscript>O–BaO–Ga<Subscript>2</Subscript>O<Subscript>3</Subscript>–SiO<Subscript>2</Subscript> system

The specific conductivity and tracer of diffusion of sodium and barium ions have been determined and the values of the transport numbers and correlation factor for diffusion have been calculated in two melts of the Na₂O–BaO–Ga₂O₃–SiO₂ system.     

Morphological and electrochemical investigation of RuO<Subscript>2</Subscript>–Ta<Subscript>2</Subscript>O<Subscript>5</Subscript> oxide films prepared by the Pechini–Adams method

Preparation methods can profoundly affect the structural and electrochemical properties of electrocatalytic coatings. In this investigation, RuO₂–Ta₂O₅ thin films containing between 10 and 90 at.% Ru were prepared by the Pechini–Adams method. These coatings were electrochemically and physically characterized by cyclic voltammetry, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). The composition and morphology of the oxide were investigated before and after accelerated life tests (ALT) by EDX and SEM. SEM results indicate typical mud-flat-cracking morphology for the majority of the films. High resolution SEMs reveal that pure oxide phases exhibit nanoporosity while binary compositions display a very compact structure. EDX analyses reveal considerable amounts of Ru in the coating even after total deactivation. XRD indicated a rutile-type structure for RuO₂ and orthorhombic structure for Ta₂O₅. XPS data demonstrate that the binding energy of Ta is affected by Ru addition in the thin films, but the binding energy of Ru is not likewise influenced by Ta. The stability of the electrodes was evaluated by ALT performed at 750 mA cm⁻² in 80 °C 0.5 mol dm⁻³ H₂SO₄. The performance of electrodes prepared by the Pechini–Adams method is 100% better than that of electrodes prepared by standard thermal decomposition.     

Optimization of Ti/SnO<Subscript>2</Subscript>–Sb<Subscript>2</Subscript>O<Subscript>5</Subscript> anode preparation for electrochemical oxidation of organic contaminants in water and wastewater

The preparation of antimony-doped tin oxide anodes on a titanium substrate (Ti/SnO₂–Sb₂O₅ anodes) by dipping in a solution of tin chloride and antimony chloride and annealing at high temperatures was optimized for the potential applications of drinking water disinfection, wastewater effluent disinfection, and industrial waste stream treatment. The effectiveness of Ti/SnO₂–Sb₂O₅ anodes prepared under different conditions was evaluated by using hexanol as a probe molecule to measure the extent of oxidative reactions, and anode performance was monitored by cyclic voltammetry. A large factorial matrix consisting of tin chloride concentration × antimony chloride concentration × annealing temperature was first evaluated, and the optimum conditions were found to be 20% tin chloride and 1% antimony chloride in the dip solution and an annealing temperature of 500°C. Further investigation showed that the rate of withdrawal from the dip solution, the number of coatings of the dip solution, and the addition of oxygen during annealing did not significantly affect anode performance. Under optimum preparation conditions, Ti/SnO₂–Sb₂O₅ anodes showed no loss of performance over 1,280 cycles of cyclic voltammetry, suggesting that their performance can be sustained over long periods of use. The result of this research is a simple preparation method for effective and long-lived Ti/SnO₂–Sb₂O₅ anodes; this method could be easily adopted by a utility for pilot- or full-scale disinfection of water and wastewater and the treatment of industrial waste streams.     

Stable multilayer TiO<Subscript>2</Subscript>–SiO<Subscript>2</Subscript> coatings for antireflection applications

In this paper, multilayer TiO₂–SiO₂ containing polydimethylsiloxane (PDMS) coatings were produced by using sol-gel method. To further investigate, the effect of triton as a non-ionic surfactant on PDMS modified single and multilayer silica and titania coatings was studied. The results showed stability of optical triton containing coatings disappears with time due to this material improve the wetting properties of PDMS sols and helps to instability by water absorption. But without triton, antireflective multilayer coatings with high transmittance 98% and excellent durability were obtained by using PDMS as additive material. This coating can be used as well as in solar applications.     

Effect of temperature on the synthesis of nanoparticles with different morphology in the system MgO–SiO<Subscript>2</Subscript>–TiO<Subscript>2</Subscript>–H<Subscript>2</Subscript>O under hydrothermal conditions

Nanoparticles with different morphology have been obtained by hydrothermal method in the system MgO–SiO₂–TiO₂–H₂O. It has been found that in the investigated temperature–time interval the formation of nanotubes of hydrosilicate with the structure of chrysotile with a small amount of impurity phases predominantly takes place.     

Vitreous region and properties of glasses of the Ga<Subscript>2</Subscript>S<Subscript>3</Subscript>–GeS<Subscript>2</Subscript>–PbF<Subscript>2</Subscript> system

Vitrification in the Ga₂S₃–GeS₂–PbF₂ system is considered. The physicochemical properties of glasses, such as density, microhardness, electroconductivity, refraction index, and transmission percentage of specimens in visible and IR ranges of spectrum are studied; differential thermal analysis is carried out; and Raman and electron paramagnetic resonance spectra are investigated.     

Study on flame structures and emissions of CO and NO in Various CH<Subscript>4</Subscript>/O<Subscript>2</Subscript>/N<Subscript>2</Subscript>–O<Subscript>2</Subscript>/N<Subscript>2</Subscript> counterflow premixed flames

An oxygen-diluted partially premixed/oxygen-enriched supplemental combustion (ODPP/OESC) counterflow flame is studied in this paper. Flame images are obtained through experiments and numerical simulations with the GRI-Mech 3.0 chemistry. The oxygen dilution effects are revealed by comparing the flame structures and emissions with those of a premixed flame and partially premixed flame (PPF) at the same equivalence ratio (?_Σ = 0.95 and ? _f = 1.4). The results show that both PPF and ODPP/OESC flames have distinct double flame structures; however, the location of the premixed combustion zone and the distance between premixed/nonpremixed combustion zone are significantly different for these two cases. For the ODPP/OESC flame, the temperature in the premixed combustion zone is lower and the premixed zone itself is located farther downstream from the fuel nozzle, which leads to reduction of NO and CO emissions, as compared to those of the PPF. Therefore, by adjusting the distribution of the oxygen concentration in the premixed and nonpremixed combustion zones, the ODPP/OESC can effectively balance the chemical reaction rate in the entire combustion zone and, consequently, reduce emissions.