Thermal and neutron shielding properties of <Superscript>10</Superscript>B<Subscript>2</Subscript>O<Subscript>3</Subscript>/polyimide hybrid materials

In this study, ¹⁰B₂O₃/polyimide (PI) hybrid materials were synthesized with the aim to improve their thermal stability and neutron shielding properties. 3,3′-Diaminodiphenyl sulfone (DADPS) reacted with 3,3′,4,4′-benzophenonetetracarboxylic dianhydride (BTDA) in N-methyl-2-pyrrolidone (NMP) and mixed with amine functionalized ¹⁰B₂O₃ to prepare a series of poly (amic acid), meanwhile, corresponding PIs were obtained via the thermal imidization procedures. The morphologies and structures of the prepared hybrid materials were characterized by scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FT-IR). The thermooxidative and flame retardancy properties of the PI films were examined by thermogravimetric analysis (TGA) and limiting oxygen ındex (LOI). The experimental results showed that as the amount of functionalized ¹⁰B₂O₃ was increased, flame retardant properties of the hybrid films were increased. Hybrid materials were also irradiated with thermal neutrons. The neutron shielding properties increasing depends on the amount and the distribution of the ¹⁰B isotope.     

Microstructure and properties of novel ReO<Subscript>2</Subscript> /polyimide nanocomposite films

A series of Rhenium (VII, Re⁷⁺) compound-doped polyimide (PI) nanohybrid films had been successfully fabricated from methyltrioxorhenium (MTO) and polyamic acid (PAA) via the solution direct-dispersing method, followed by a stepwise thermal imidization process. X-ray photoelectron spectroscopy (XPS) confirmed that MTO had decomposed into Re (IV) oxidation state (ReO₂). Field emission scanning electron microscopy (FE-SEM) showed that for the differrent hybrid films, the ReO₂ nanoparticles which formed by MTO decomposing well dispersed in polyimide matrix with a size of 40–60 nm. Thermal analysis indicated that the introduction of MTO decreased the thermal stability and the glass transition temperature (T_g) because of the unstable MTO. DMTA and static tensile measurements showed that the storage modulus and the elongation at break of nanocomposite films had a maximum value when the 1% of MTO was doped in PI, while the tensile strength decreased with increasing MTO content on the whole.     

Li<Subscript>2</Subscript>Cu<Subscript>2</Subscript>(MoO<Subscript>4</Subscript>)<Subscript>3</Subscript>/TiO<Subscript>2</Subscript> + SiO<Subscript>2</Subscript>/Ti compositions for the catalytic afterburning of diesel soot

Two methods were used to obtain a catalytically active oxide coating on the surface of titanium for the catalytic afterburning of diesel soot: plasma electrochemical formation of an oxide film on the surface of titanium and extraction pyrolytic deposition of the Li₂Cu₂(MoO₄)₃ compound. The Li₂Cu₂(MoO₄)₃/TiO₂ + SiO₂/Ti compositions synthesized by the single-step extraction pyrolytic treatment of the oxidized surface of titanium ensured a high burning rate of soot of ∼300°C. The subsequent deposition of Li₂Cu₂(MoO₄)₃ lowers the activity of the catalyst, due probably to the growth of molybdate phase crystallites and the filling of open oxide film pores. Double lithium-copper molybdate is able to reduce appreciably the concentration of CO in the oxidation products of soot. The advantages of these methods are the possibility of forming high-cohesion durable coatings on surfaces of any complexity, the simplicity of their implementation, and high productivity and low cost. The obtained results can be recommended for use in developing methods for creating composite coatings on catalytic soot filters.     

Nanostructured composite ceramic materials in the ZrO<Subscript>2</Subscript>-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> system

The composite ceramic materials based alumina and zirconia in the monoclinic form (10 wt %) or the tetragonal form stabilized by yttrium (7–45 wt %) are produced from metastable nanopowders through magnetic pulsed compaction followed by free sintering. The specific features revealed in the shrinkage are investigated at temperatures in the range 1400–1500°C. The development of the microstructure and polymorphic transformations are analyzed using X-ray diffraction and atomic-force microscopy. The fracture toughness and the microhardness of the samples are determined by the indentation technique.     

Separation characteristics of tetrapropylammoniumbromide templating silica/alumina composite membrane in CO<Subscript>2</Subscript>/N<Subscript>2</Subscript>, CO<Subscript>2</Subscript>/H<Subscript>2</Subscript> and CH<Subscript>4</Subscript>/H<Subscript>2</Subscript> systems

Nanoporous silica membrane without any pinholes and cracks was synthesized by organic templating method. The tetrapropylammoniumbromide (TPABr)-templating silica sols were coated on tubular alumina composite support ( γ-Al₂O₃/ α-Al₂O₃ composite) by dip coating and then heat-treated at 550 °C. By using the prepared TPABr templating silica/alumina composite membrane, adsorption and membrane transport experiments were performed on the CO₂/N₂, CO₂/H₂ and CH₄/H₂ systems. Adsorption and permeation by using single gas and binary mixtures were measured in order to examine the transport mechanism in the membrane. In the single gas systems, adsorption characteristics on the α-Al₂O₃ support and nanoporous unsupport (TPABr templating SiO₂/ γ-Al₂O₃ composite layer without α-Al₂O₃ support) were investigated at 20–40 °C conditions and 0.0–1.0 atm pressure range. The experimental adsorption equilibrium was well fitted with Langmuir or/and Langmuir-Freundlich isotherm models. The α-Al₂O₃ support had a little adsorption capacity compared to the unsupport which had relatively larger adsorption capacity for CO₂ and CH₄. While the adsorption rates in the unsupport showed in the order of H₂> CO₂> N₂> CH₄ at low pressure range, the permeate flux in the membrane was in the order of H₂≫N₂> CH₄> CO₂. Separation properties of the unsupport could be confirmed by the separation experiments of adsorbable/non-adsorbable mixed gases, such as CO₂/H₂ and CH₄/H₂ systems. Although light and non-adsorbable molecules, such as H₂, showed the highest permeation in the single gas permeate experiments, heavier and strongly adsorbable molecules, such as CO₂ and CH₄, showed a higher separation factor (CO₂/H₂=5-7, CH₄/H₂=4-9). These results might be caused by the surface diffusion or/and blocking effects of adsorbed molecules in the unsupport. And these results could be explained by surface diffusion. This paper is dedicated to Professor Hyun-Ku Rhee on the occasion of his retirement from Seoul National University.     

Thermal behavior of reedmergnerite NaBSi<Subscript>3</Subscript>O<Subscript>8</Subscript> and searlesite NaBSi<Subscript>2</Subscript>O<Subscript>5</Subscript>(OH)<Subscript>2</Subscript>

The results of studying the thermal behavior of natural boron albite–reedmergnerite NaBSi₃O₈ and aqueous boricilicate–searlesite NaBSi₂O₅(OH)₂ obtained by the method of hydrothermal synthesis are presented. In the investigated temperature range, reedmergnerite (30–780°C) does not undergo phase transformations. Thermal expansion is sharply anisotropic, which is a characteristic feature of the expansion of feldspars. Aqueous borosilicate searlesite (25–750°C) is amorphized above 400°C as a result of dehydration and cristobalite crystallizes from the amorphous phase. The expansion of searlesite is relatively isotropic.     

Preparation of asymmetric polysulfone/polyimide blended membranes for CO<Subscript>2</Subscript> separation

Asymmetric Flat sheet polysulfone-polyimide (PSF-PI) blended polymeric membranes (with PI content from 5–20%) have been fabricated following phase inversion technique. The membranes have been thoroughly characterized by the measurement of porosity, mechanical properties and also by SEM, FTIR and DSC analyses. With the increase in the PI content, the mechanical properties of the membranes, like Young’s modulus, tensile strength and elongation at break, increased. SEM investigations revealed that the surfaces of fabricated blended membranes possessed adequate homogeneity and their cross-sections showed non-porous top and diminutive porous substructure. From DSC analyses it has been observed that different compositions of the blended membranes exhibited single glass transition temperatures, implying proper compatibility of the polymers. The permeance of CO₂ and CH₄ through the membrane increased with the increase in PI content and it gradually decreased with the increase in the feed pressure in the range of 2–10 bar. Under the present investigation, the membrane with 20% PI content exhibited the maximum selectivity for the separation of CO₂/CH₄ gas mixes.     

Degradation kinetics of recalcitrant organic compounds in a decontamination process with UV/H<Subscript>2</Subscript>O<Subscript>2</Subscript> and UV/H<Subscript>2</Subscript>O<Subscript>2</Subscript>/TiO<Subscript>2</Subscript> processes

In this study, degradation aspects and kinetics of organics in a decontamination process were considered in the degradation experiments of advanced oxidation processes (AOP),i.e., UV, UV/H₂O, and UV/H₂O,/TiO₂ systems. In the oxalic acid degradation with different H₂O₂ concentrations, it was found that oxalic acid was degraded with the first order reaction and the highest degradation rate was observed at 0.1 M of hydrogen peroxide. Degradation rate of oxalic acid was much higher than that of citric acid, irrespective of degradation methods, assuming that degradation aspects are related to chemical structures. Of methods, the TiO₂ mediated photocatalysis showed the highest rate constant for oxalic acid and citric acid degradation. It was clearly showed that advanced oxidation processes were effective means to degrade recalcitrant organic compounds existing in a decontamination process.     

Photoreduction of CO<Subscript>2</Subscript> into CH<Subscript>4</Subscript> using Bi<Subscript>2</Subscript>S<Subscript>3</Subscript>-TiO<Subscript>2</Subscript> double-layered dense films

Nano-sized bismuth sulfide (Bi₂S₃) and titanium dioxide (TiO₂) with the orthorhombic and anatase tetragonal structures, respectively, were synthesized for application as catalysts for the reduction of carbon dioxide (CO₂) to methane (CH₄). Four double-layered dense films were fabricated with different coating sequences—TiO₂ (bottom layer)/Bi₂S₃ (top layer), Bi₂S₃/TiO₂, TiO₂/Bi₂S₃: TiO₂ (1 : 1) mix, and Bi₂S₃: TiO₂ (1 : 1) mix/Bi₂S₃: TiO₂ (1 : 1) mix—and applied to the photoreduction of CO₂ to CH₄; the catalytic activity of the fabricated films was compared to that of the pure TiO₂/TiO₂ and Bi₂S₃/Bi₂S₃ doubled-layered films. The TiO₂/Bi₂S₃ double-layered film exhibited superior photocatalytic behavior, and higher CH₄ production was obtained with the TiO₂/Bi₂S₃ double-layered film than with the other films. A model of the mechanism underlying the enhanced photoactivity of the TiO₂/Bi₂S₃ double-layered film was proposed, and it was attributed in effective charge separation.     

Study of electrochemical properties and the charge/discharge mechanism for Li<Subscript>4</Subscript>Mn<Subscript>5</Subscript>O<Subscript>12</Subscript>/MnO<Subscript>2</Subscript>-AC hybrid supercapacitor

Spinel Li₄Mn₅O₁₂ was prepared by a sol–gel method. The manganese oxide and activated carbon composite (MnO₂-AC) were prepared by a method in which KMnO₄ was reduced by activated carbon (AC). The products were characterized by XRD and FTIR. The hybrid supercapacitor was fabricated with Li₄Mn₅O₁₂ and MnO₂-AC, which were used as materials of the two electrodes. The pseudocapacitance performance of the Li₄Mn₅O₁₂/MnO₂-AC hybrid supercapacitor was studied in various aqueous electrolytes. Electrochemical properties of the Li₄Mn₅O₁₂/MnO₂-AC hybrid supercapacitor were studied by using cyclic voltammetry, electrochemical impedance measurement, and galvanostatic charge/discharge tests. The results show that the hybrid supercapacitor has electrochemical capacitance performance. The charge/discharge test showed that the specific capacitance of 51.3 F g⁻¹ was obtained within potential range of 0–1.3 V at a charge/discharge current density of 100 mA g⁻¹ in 1 mol L⁻¹ Li₂SO₄ solution. The charge/discharge mechanism of Li₄Mn₅O₁₂ and MnO₂-AC was discussed.     

Investigation into the formation of phases with a Ba<Subscript>2</Subscript>Ti<Subscript>9</Subscript>O<Subscript>20</Subscript>-type structure in the BaO-TiO<Subscript>2</Subscript> and BaO-SrO-TiO<Subscript>2</Subscript> systems

The mechanism of formation of barium titanate Ba₂Ti₉O₂₀ in the BaO-TiO₂ and BaO-SrO-TiO₂ systems is investigated using initial mixtures prepared by three methods, namely, mechanical grinding of the initial reactants, coprecipitation from aqueous solutions of salts, and the sol-gel technique. It is established that, irrespective of the preparation procedure, the formation of Ba₂Ti₉O₂₀ proceeds through the formation of the intermediate phases BaTi₄O₉ and BaTi₅O₁₁. The nature of the intermediate phases is determined by the homogeneity and dispersion of the initial mixture, as well as by the stability of the intermediate phase. The most optimum conditions for the synthesis of Ba₂Ti₉O₂₀ are provided by the formation of BaTi₅O₁₁ as an intermediate phase upon heat treatment of the coprecipitation products in the nanocrystalline state. The metastability and structural defects in the BaTi₅O₁₁ intermediate phase encourage a decrease in the temperature of the final heat treatment by 100–150°C in the course of the preparation of Ba₂Ti₉O₂₀ single-phase ceramics.     

Investigation into the phase formation in the ZrO<Subscript>2</Subscript>-CeO<Subscript>2</Subscript> system

Nanopowders of solid solutions with different compositions are prepared in the zirconia-enriched region of the ZrO₂-CeO₂ system. The crystallization of these powders and the formation of the monoclinic, cubic, and tetragonal solid solutions of the composition (Zr_{1 – x} Ce_x)O₂ are investigated. It is found that the unit cell parameters of the solid solutions increase as the cerium content increases. This confirms the fact that cerium ions [r(Ce⁴⁺) = 1.11 ] substitute for zirconium ions [r(Zr⁴⁺) = 0.98 ] in these solid solutions. The average size of crystallites of the solid solutions under investigation increases from 5 to 60 nm in the temperature range 500–1200°C.Original Russian Text Copyright © 2005 by Fizika i Khimiya Stekla, Panova, Glushkova, Nefedova.     

An investigation into the conversion of In<Subscript>2</Subscript>O<Subscript>3</Subscript> into InN nanowires

Straight In₂O₃ nanowires (NWs) with diameters of 50 nm and lengths ≥2 μm have been grown on Si(001) via the wet oxidation of In at 850°C using Au as a catalyst. These exhibited clear peaks in the X-ray diffraction corresponding to the body centred cubic crystal structure of In₂O₃ while the photoluminescence (PL) spectrum at 300 K consisted of two broad peaks, centred around 400 and 550 nm. The post-growth nitridation of In₂O₃ NWs was systematically investigated by varying the nitridation temperature between 500 and 900°C, flow of NH₃ and nitridation times between 1 and 6 h. The NWs are eliminated above 600°C while long nitridation times at 500 and 600°C did not result into the efficient conversion of In₂O₃ to InN. We find that the nitridation of In₂O₃ is effective by using NH₃ and H₂ or a two-step temperature nitridation process using just NH₃ and slower ramp rates. We discuss the nitridation mechanism and its effect on the PL.     

Synthetic spinels of the system MgO-Cr<Subscript>2</Subscript>O<Subscript>3</Subscript>-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>

Synthetic spinels of the system MgO-Cr₂O₃-Al₂O₃-Fe₂O₃ are considered and the desirability of organizing their production for the refractory industry is demonstrated. Translated from Novye Ogneupory, No. 6, pp. 32–35, June 2008.     

Photocatalytic activity of metal-decorated SiO<Subscript>2</Subscript>@TiO<Subscript>2</Subscript> hybrid photocatalysts under water splitting

We report the fabrication of a metal-decorated hybrid nanocomposite with TiO₂ encapsulation (Metal/SiO₂@TiO₂, Metal=Pt or Ru) using a simple surface-modification chemical process. Metal nanoparticles capped with polyvinylpyrrolidone were successfully assembled on functionalized SiO₂ via electrostatic interactions, after which a thin layer of TiO₂ was coated on the surface by the sol-gel process to avoid agglomeration of the coated silica spheres. Transmission electron microscopy studies confirmed that the metal nanoparticles were uniformly distributed throughout the surface of the SiO₂ with a thin layer of TiO₂. In addition, X-ray diffraction was employed to ensure the crystal structure of the uniformly coated thin TiO₂ layer. Even after calcination at 500 °C, the structure remained intact, confirming high thermal stability. The photocatalytic activity of the metal-decorated SiO₂/TiO₂ nanocomposites was evaluated using the H₂ evolution reaction. The Metal/SiO₂@TiO₂ catalysts show the photocatalytic water splitting efficiency for H₂ generation (i.e., 0.14% for Pt/SiO₂@TiO₂ and 0.12% for Ru/SiO₂@TiO₂), while there is no generation of H₂ on the Metal/SiO₂ without a coating layer. These results indicate that the anatase crystalline coating layer has good thermal and chemical stability and plays a significant role in photocatalytic H₂ production.     

Electrical conductivity and structure of glasses in the Na<Subscript>2</Subscript>O-Na<Subscript>2</Subscript>S-P<Subscript>2</Subscript>O<Subscript>5</Subscript> and Na<Subscript>2</Subscript>S-P<Subscript>2</Subscript>S<Subscript>5</Subscript> systems

The glasses, in which oxygen was partially replaced with sulfur, have been synthesized in the Na₂O-P₂O₅-Na₂S system. The chemical and chromatographic analyses of the glasses synthesized have been performed. The temperature-concentration dependences of electrical conductivity of the glasses have been studied over a wide temperature range; the glass transition temperatures and the nature of charge carriers have been determined. The IR spectra and Raman spectra have been recorded at room temperature; the density and microhardness of the glasses and ultrasound velocity have been measured. A comparison of the electrical conductivities of the investigated glasses with those of the earlier studied glasses in the Na₂O-P₂O₅ system has shown their fair coincidence. The introduction of sodium sulfide into the Na₂O-P₂O₅ system is accompanied by an approximately threefold increase in electrical conductivity, although the concentrations of charge carriers (sodium ions) in the glasses amount to ∼17 and ∼26 mmol/cm³, respectively. The rise in electrical conductivity has been assumed to be caused by the increase in the degree of dissociation of polar structural chemical units including sulfide ions and by the higher mobility of sodium ions in the oxygen-free matrix.     

Low-temperature anti-icing reagents in the Ca(NO<Subscript>3</Subscript>)<Subscript>2</Subscript>-Mg(NO<Subscript>3</Subscript>)<Subscript>2</Subscript>-CO(NH<Subscript>2</Subscript>)<Subscript>2</Subscript>-H<Subscript>2</Subscript>O system and their properties

The polytherms of ice melting in sections of the Ca(NO₃)₂-Mg(NO₃)₂-CO(NH₂)₂-H₂O system with different component ratios were studied in the temperature interval from 0 to −40°C. A series of nitrate and nitrate-carbonate reagents that are promising for the creation of anti-acing reagents were found, which form eutectics with ice at temperatures from −25 to −39°C. Their properties, viz., melting properties with respect to ice and corrosiveness on metals and alloys, were determined. An effective corrosion inhibitor was selected.     

Simultaneous absorption of CO<Subscript>2</Subscript> and SO<Subscript>2</Subscript> into aqueous AMP/NH<Subscript>3</Subscript> solutions in binary composite absorption system

To enhance the absorption rate for CO₂ and SO₂, aqueous ammonia (NH₃) solution was added to an aqueous 2-amino-2-methyl-1-propanol (AMP) solution. The simultaneous absorption rates of AMP and a blend of AMP+ NH₃ for CO₂ and SO₂ were measured by using a stirred-cell reactor at 303 K. The process operating parameters of interest in this study were the solvent and concentration, and the partial pressures of CO₂ and SO₂. As a result, the addition of NH₃ solution into aqueous AMP solution increased the reaction rate constants of CO₂ and SO₂ by 144 and 109%, respectively, compared to that of AMP solution alone. The simultaneous absorption rate of CO₂/SO₂ on the addition of 1 wt% NH₃ into 10 wt% AMP at a p _A1 of 15 kPa and p _A2 of 1 kPa was 5.50×10⁻⁶ kmol m⁻² s⁻¹, with an increase of 15.5% compared to 10 wt% AMP alone. Consequently, the addition of NH₃ solution into an aqueous AMP solution would be expected to be an excellent absorbent for the simultaneous removal of CO₂/SO₂ from the composition of flue gas emitted from thermoelectric power plants.     

Partial oxidation of methane over Ni/Ce-Zro<Subscript>2</Subscript>/θ-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>

The catalytic behavior of Ni/Ce-ZrO₂/θ-Al₂O₃ has been investigated in the partial oxidation of methane (POM) toward synthesis gas. The catalyst showed high activity and selectivity due to the heat treatment of the support and the promotional effect of Ce-ZrO₂. It is suggested that the support was stabilized through the heat treatment of γ-Al₂O₃ and the precoating of Ce-ZrO₂, on which a protective layer was formed. Moreover, sintering of the catalyst was greatly suppressed for 24 h test. Pulse experiments of CH₄, O₂ and/or CH₄/O₂ with a molar ratio of 2 were systematically performed over fresh, partially reduced and well reduced catalyst. Results indicate that CH₄ can be partially oxidized to CO and H₂ by the reactive oxygen in complex NiO_x species existing over the fresh catalyst. It is demonstrated that POM over Ni/Ce-ZrO₂/θ-Al₂O₃ follows the pyrolysis mechanism, and both the carbonaceous materials from CH₄ decomposition over metallic nickel and the reactive oxygen species present on NiO_x and Ce-ZrO₂ are intermediates for POM.