Behavior of melts in the UO<Subscript>2</Subscript>-SiO<Subscript>2</Subscript> system in the liquid-liquid phase separation region

The behavior of melts in the uranium oxide-silicon dioxide system is experimentally investigated in air upon induction melting in a “cold crucible.” The existence of the two-phase liquid region in this system is confirmed. It is demonstrated that the melts absorb oxygen from air, which leads to crystallization of the UO_2.25 compound upon cooling. In the case of considerable internal heat release, sharp cooling of the melt surface results in the liberation of gas, which brings about bulging and, sometimes, melt ejection from the crucible.     

Experimental investigation and thermodynamic simulation of the uranium oxide–zirconium oxide–iron oxide system in air

The behavior of melts and the phase composition of crystallization products of six compositions in the uranium oxide-zirconium oxide-iron oxide system in air have been investigated. It has been revealed that crystallized samples containing 20–50 wt % uranium oxide and 25–80 wt % iron oxide (the rest is zirconium oxide) consist of five crystalline phases and involve two types of eutectic structures. The possible factors responsible for this phenomenon have been considered.     

Efficient gas phase photodecomposition of acetone by Ru-doped Titania

Nanocrystalline titania particles doped with ruthenium oxide have been prepared by homogenous hydrolysis of TiOSO₄ in aqueous solutions in the presence of urea. The synthesized particles were characterized by X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), High Resolution Transmission Electron Microscopy (HRTEM), Selected Area Electron Diffraction (SAED) and surface area (BET) and porosity determination (BJH). The photocatalytic activity of Ru-doped titania samples was determined in the gas phase by decomposition of acetone during irradiation at 365 nm and 400 nm. The Ru-doped titania samples demonstrated enhanced photocatalytic activity under visible light. Ruthenium oxide causes the anatase to rutile transformation to occur at lower temperatures and decreasing of band-gap energy of Ru-doped samples.     

Photodegradation of DMMP and CEES on zirconium doped titania nanoparticles

The structure and photocatalytic activity of Zr doped TiO₂ nanocrystallites with a varying Zr content between 0 and 15 wt% prepared by an efficient and environmentally benign method has been studied by vibrational spectroscopy, TEM and XRD. It is shown that the presence of Zr⁴⁺ ions stabilizes the anatase structure and delays phase transformation to rutile upon annealing as well as retarding grain coarsening. All TiO₂ samples up to 13 wt% Zr doping concentration show better or similar photoreactivity compared to P25 (Degussa) for decomposition of adsorbed 2-chloroethyl ethyl sulphide (CEES) and dimethyl methylphosphonate (DMMP) in synthetic air at room temperature. The most efficient sample for photodegradation of both CEES and DMMP is shown to be titania doped with 6.8 wt% Zr. The photodegradation of CEES is faster than DMMP under the same experimental conditions. On the undoped TiO₂ sample urea residues are detected spectroscopically. Much less is detected on the Zr doped samples. Mode resolved in situ FTIR surface spectroscopy enables distinction of CEES or DMMP, decomposition products as well as the influence of residues from the particle synthesis. This facilitates extraction of intra-comparable reaction rates. Possible explanations for the improved reactivity of the Zr doped titania are discussed.     

Phase equilibria during crystallization of melts in the uranium oxide-iron oxide system in air

The uranium oxide-iron oxide system is investigated. It is revealed that, upon both quenching and slow cooling of samples after their melting in air, the solid phase contains five crystalline phases, such as the oxide of quadruply charged uranium UO₂, the mixed oxide UO_2.66(U₃O₈), hematite FeO_1.5(Fe₂O₃ ), magnetite Fe_1.33(Fe₃O₄), and the binary compound Fe²⁺U⁶⁺O₄.     

Reaction of sulfur mustard gas,soman and agent VX with nanosized anatase TiO2 and ferrihydrite

Homogeneous hydrolysis of titanium oxo‐sulfate and iron(III) sulfate has been used to prepare anatase TiO₂ and ferrihydrite with high specific surface area. Resulting samples were characterised by specific surface area (Brunauer–Emmett–Teller method) and porosity (Barrett–Joyner–Halenda method) measurements, X‐ray powder diffraction (XRD) and scanning electron microscopy (SEM). The samples of anatase TiO₂ and ferrihydrite were evaluated for their ability to degrade chemical warfare agents (sulfur mustard gas, soman and agent VX) to non‐toxic products. The largest percentage of mustard gas converted into non‐toxic products after the completion of the reaction was 99%. Copyright © 2005 Society of Chemical Industry     

Synthesis of spherical metal oxide particles using homogeneous precipitation of aqueous solutions of metal sulfates with urea

Spherical micron sized porous particles of goethite FeO(OH), boehmite AlO(OH), anatase TiO₂, Zn(OH)₂ and binary mixtures of these oxides have been synthesized by homogeneous precipitation from aqueous solution containing urea in the presence of corresponding metal sulfates. Metal (hydrous) oxide particles obtained show spherical morphology and consist of agglomerated randomly oriented nanocrystallites. Synthesized metal oxide hydroxides were characterized using Brunauer-Emmett-Teller (BET) surface area and Barrett-Joiner-Halenda porosity (BJH), X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and energy-dispersive X-ray microanalysis (EDX).     

Zirconium doped nano-dispersed oxides of Fe,Al and Zn for destruction of warfare agents

Zirconium doped nano dispersive oxides of Fe, Al and Zn were prepared by a homogeneous hydrolysis of the respective sulfate salts with urea in aqueous solutions. Synthesized metal oxide hydroxides were characterized using Brunauer–Emmett–Teller (BET) surface area and Barrett–Joiner–Halenda porosity (BJH), X-ray diffraction (XRD), infrared spectroscopy (IR), scanning electron microscopy (SEM) and energy-dispersive X-ray microanalysis (EDX). These oxides were taken for an experimental evaluation of their reactivity with sulfur mustard (HD or bis(2-chloroethyl)sulfide), soman (GD or (3,3′-Dimethylbutan-2-yl)-methylphosphonofluoridate) and VX agent (S-[2-(diisopropylamino)ethyl]-O-ethyl-methylphosphonothionate). The presence of Zr⁴⁺ dopant can increase both the surface area and the surface hydroxylation of the resulting doped oxides, decreases their crystallites' sizes thereby it may contribute in enabling the substrate adsorption at the oxide surface thus it can accelerate the rate of degradation of warfare agents. Addition of Zr⁴⁺ converts the product of the reaction of ferric sulphate with urea from ferrihydrite to goethite. We found out that doped oxo-hydroxides Zr–FeO(OH) — being prepared by a homogeneous hydrolysis of ferric and zirconium oxo-sulfates mixture in aqueous solutions — exhibit a comparatively higher degradation activity towards chemical warfare agents (CWAs). Degradation of soman or VX agent on Zr-doped FeO(OH) containing ca. 8.3 wt.% of zirconium proceeded to completion within 30 min.     

Preparation and characterization of a reference aluminum mirror

The preparation and characterization of a reference mirror of protected aluminum (Al) is reported. The mirror is made of 50-60-nm-thick Al film, coated with several-nanometer-thick A12O5 and 30-nm-thick film of AIN. The mirror characterization is based on reliable and precise reflectance measurements relative to a silicon- (Si-) wafer reference mirror. The simple phenomenological Drude-Lorentz model is applied for modeling the dispersion relations n(lambda) and k(lambda) of the Al film. The reflection of the protected Al mirror is determined in the 400-800-nm spectral range with accuracy better than 0.01 for p- and s-polarized light at angles of incidence from 0 degrees to 70 degrees. The accuracy has been confirmed with an evaporated thin silver film with known n(lambda), k(lambda), and d derived by photometric measurements at normal light incidence.     

Photoactivity of anatase–rutile TiO2 nanocrystalline mixtures obtained by heat treatment of homogeneously precipitated anatase

Nanosized titanium dioxide photocatalysts with varying amount of anatase and rutile phases have been synthesized. Homogeneous precipitation of aqueous solutions containing TiOSO₄ with urea was used to prepare porous spherical clusters of anatase TiO_2. Photoactive titania powders with variable amount of anatase and rutile phases were prepared by heating of pure anatase in the temperatutre range 800–1150 °C. The structure evolution during heating of the starting anatase powders was studied by XRD analysis in overall temperature range of phase transformation. The morphology and microstucture characteristics were also obtained by HRTEM, BET and BJH. The spherical particle morphology of TiO₂ mixtures determined by SEM was stable in air up to 900 °C. The photocatalytic activity of the sample titania TIT85/825 heated to 825 °C in air, contained 77.4% anatase and 22.6% rutile was higher than that nanocrystalline anatase powder. Titania sample TIT85/825 reveals the highest catalytic activity during the photocatalyzed degradation of 4-chlorophenol in aqueous suspension.