Preparation of Si<Subscript>3</Subscript>N<Subscript>4</Subscript>–ZrO<Subscript>2</Subscript> ceramic composites by self-propagating high-temperature synthesis

Results are provided for a study of Si₃N₄–ZrO₂ composite ceramic material preparation by self-propagating high-temperature synthesis from ferrosilicon and zirconium concentrate. It is noted that as a result of high-temperature dissociation of ZrSiO₄ silicon dioxide is nitrided with formation of silicon oxynitride and it is condensed in surface layers of a specimen in the form of filamentary crystals.     

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.     

Structural analyses of RuO<Subscript>2</Subscript>–TiO<Subscript>2</Subscript>/Ti and IrO<Subscript>2</Subscript>–RuO<Subscript>2</Subscript>–TiO<Subscript>2</Subscript>/Ti anodes used in industrial chlor-alkali membrane processes

The morphology and composition of RuO₂–TiO₂/Ti and IrO₂–RuO₂–TiO₂/Ti anodes, which have been used for the production of chlorine for more than 10 years, were analyzed by various methods; such as high-resolution scanning electron microscopy, high-resolution Auger electron spectroscopy, electron probe X-ray emission microanalysis and X-ray diffraction analysis. Drastic changes in the surface morphology, including partial exfoliation of a small amount of the oxide layer and a reduction in the content of ruthenium species through dissolution, were observed for the RuO₂–TiO₂/Ti anode. For the IrO₂–RuO₂–TiO₂/Ti anode, on the other hand, there were moderate changes in the surface morphology and moderate dissolution of iridium and ruthenium species.     

Advanced modelling of self-propagating high-temperature synthesis: the case of the Ti–C system

A novel mathematical model to simulate SHS processes is proposed. Based on the so-called enthalpy approach to properly account for phase transitions, the model describes microstructural evolution using suitable population balances. For the case of the synthesis of TiC from pure Ti and C, the model quantitatively interprets that reactants are heated up to the Ti melting point. Once Ti melting occurs, the melt is redistributed within the porous system, thus increasing the contact area between reactants and favoring graphite dissolution. TiC grains are then modelled as nucleating in the melt and then growing until the final microstructure is reached. Model reliability is tested by comparison with experimental data.     

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.     

Synthesis of the study of solid solutions based on the ZrO<Subscript>2</Subscript>–HfO<Subscript>2</Subscript>–Y<Subscript>2</Subscript>O<Subscript>3</Subscript>(CeO<Subscript>2</Subscript>) system

The results of the studies of the conditions of the liquid-phase synthesis of highly dispersed xerogels with a low degree of agglomeration and precursor nanopowders (~10–12 nm) based on zirconium dioxide in the ZrO₂–HfO₂–Y₂O₃(CeO₂) system are presented. The thermal decomposition of xerogels and formation of crystalline solid solutions with the structure of fluorite are investigated. The optimal conditions for the solidification of nanodispersed powders for fabricating compact ceramics based on solid solutions of ZrO₂ and the physical–chemical properties of these ceramics are studied.     

Si-filled ceramic composite by thermal explosion in the Al–SiO<Subscript>2</Subscript> system

Si-filled ceramic composite was prepared through thermal explosion in the Al–SiO₂ system. The material can be expected to find its application to reprocessing quartz wastes into cermets to be used in microelectronic devices.     

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.     

Synthesis and comparative studies of xerogels,aerogels, and powders based on the ZrO<Subscript>2</Subscript>–Y<Subscript>2</Subscript>O<Subscript>3</Subscript>–СeO<Subscript>2</Subscript> system

The technology of liquid-phase synthesis of mesoporous xerogels and aerogels based on ZrO₂–Y₂O₃–CeO₂ is developed. Xerogels are obtained by the coprecipitation of hydroxides, while aerogels are obtained in accordance with the sol–gel technology: the average pore size is 1.5–17.2 nm and the specific surface area is 120–878 m²/g. Aerogels are characterized by a high degree of porosity: the pore volume attains 1–4 cm³/g. Based on precursor xerogels, nanopowders of a tetragonal solid solution of the (ZrО₂)_0.92(Y₂О₃)_0.03(CeО₂)_0.05 composition with a particle size of 5–9 nm and S _spec = 74 m²/g were fabricated. Due to the high values of their specific surface area, the synthesized xerogels and aerogels are promising as sorbents, catalysts, or catalyst supports.     

Synthesis and physicochemical properties of a solid oxide nanocomposite based on a ZrO<Subscript>2</Subscript>–Y<Subscript>2</Subscript>O<Subscript>3</Subscript>–Gd<Subscript>2</Subscript>O<Subscript>3</Subscript>–MgO system

A highly dispersive powder with a (ZrO₂)_0.92(Y₂O₃)_0.03(Gd₂O₃)_0.03(MgO)_0.02 composition and specific surface area of 150 m²/g has been synthesized via a method of coprecipitation of hydroxides with the subsequent cryochemical treatment of the gel. Nanoceramics based on the cubic modification of zirconium dioxide with the grain size of ~40–45 nm have been obtained. The temperature dependence of the specific electrical conductance of the nanoceramics within a temperature range of 350–870°C in air has been studied, and the ratio of the ionic and electronic parts of the conductance has been determined. Recommendations for the use of the obtained oxide nanocomposite as an electrolyte for a high-temperature fuel cell have been given.     

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.     

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 of the physicomechanical properties of modified material of the composition Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–SiC–C based on acpb after reduction annealing

Dependences of the apparent density and ultimate strength in compression on amount of silicon carbide and form of modifying addition (Al, Si, B and other mixes) for materials of the composition Al2O3–SiC–C based on an aluminochromium phosphate binder after firing in a reducing atmosphere at 1400°C are studied. It is established that addition of amorphous boron and Al + Si + B are effective for improving physicomechanical properties.     

Effect of the relative volume of the conducting phase on the electroconductivity of glasses in the Na<Subscript>2</Subscript>O–B<Subscript>2</Subscript>O<Subscript>3</Subscript>–SiO<Subscript>2</Subscript> system

The effect of the relative volume of the conducting phase on the electroconductivity of phase-separated glasses in the ternary system Na₂O–B₂O₃–SiO₂, whose compositions are on the same glass transition isotherm at 550°C, is investigated. It is demonstrated that the electroconductivity of phase-separated sodium borosilicate glasses does not depend on the relative volume of the conducting phase (within the limits from 0.3 to 0.9) under the condition that its composition invariable.     

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.     

Synthesis and characterization of nanocomposites Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>–SiO<Subscript>2</Subscript>–chitosan based on lbl technology

In this paper, the apparent chain-like core-shell structure Fe₃O₄–SiO₂–chitosan nanoparticles was synthesized by two-step method with cross-linking action of glutaraldehyde based on layer-by-layer technology, the composite particles were characterized by IR, XRD, TEM, SEM, EDS and VSM analytical methods, and the synthesis conditions of the product were studied. The results indicated that the diameter of the composite particles is about 106.5 nm, the parietal layer of chitosan is 20 nm, and after crosslinking action of glutaraldehyde, chitosan uniformaly coated the outer surface of Fe₃O₄–SiO₂.     

Porous ceramics based on the ZrO<Subscript>2</Subscript>(Y<Subscript>2</Subscript>O<Subscript>3</Subscript>)–Al<Subscript>2</Subscript>O<Subscript>3</Subscript> system for filtration membranes

The results of the studies of the process of fabricating ceramic filtration membranes in the system ZrO₂(Y₂O₃)–Al₂O₃ are presented. The phase compositions of the precursor powders and sintered ceramics have been investigated and their porous structures have been determined. Two stages of the implementation of the technology were demonstrated: fabrication of substrates with an open porosity ranging from 20 to 47% and pore sizes in the 100–300 nm range, as well as the deposition of nanocrystalline aluminum oxide layers on them. It has been established that the pore size distribution in the membrane layer of α-Al₂O₃ is unimodal (from 30 to 100 nm).     

Study on the preparation of Mg–Li–Mn alloys by electrochemical codeposition from LiCl–KCl–MgCl<Subscript>2</Subscript>–MnCl<Subscript>2</Subscript> molten salt

This study presents a novel electrochemical study on the codeposition of Mg, Li, and Mn on a molybdenum electrode in LiCl–KCl–MgCl₂–MnCl₂ melts at 893 K to form different phases Mg–Li–Mn alloys. Transient electrochemical techniques such as cyclic voltammetry, chronopotentiometry, and chronoamperometry have been used in order to investigate the codeposition behavior of Mg, Li, and Mn ions. The results obtained show that the potential of Li metal deposition, after the addition of MgCl₂ and MnCl₂, is more positive than the one of Li metal deposition before the addition. The codeposition of Mg, Li, and Mn occurs at current densities lower than −1.43 A cm⁻² in LiCl–KCl–MgCl₂ (8 wt%) melts containing 2 wt% MnCl₂. The onset potential for the codeposition of Mg, Li, and Mn is −2.100 V. α, α + β, and β phases Mg–Li–Mn alloys with different lithium and manganese contents were obtained via galvanostatic electrolysis from LiCl–KCl melts with different concentrations of MgCl₂ and MnCl₂. The microstructures of typical α and β phases of Mg–Li–Mn alloys were characterized by X-ray diffraction (XRD), optical microscopy (OM), and scanning electron microscopy (SEM). The analysis of energy dispersive spectrometry (EDS) and EPMA area analysis showed that the elements of Mg and Mn distribute homogeneously in the Mg–Li–Mn alloys. The results of inductively coupled plasma analysis determined that the chemical compositions of Mg–Li–Mn alloys correspond with the phase structures of XRD patterns, and lithium and manganese contents of Mg–Li–Mn alloys depend on the concentrations of MgCl₂ and MnCl₂.