Synthesis and structural study of new potassium uranyl selenates K2(H5O2)(H3O)[(UO2)2(SeO4)4(H2O)2](H2O)4 and K3(H3O)[(UO2)2(SeO4)4(H2O)2](H2O)5

Single crystals of new uranyl selenates K₂(H₅O₂)(H₃O)[(UO₂)₂(SeO₄)₄(H₂O)₂](H₂O)₄ (1) and K₃(H₃O)[(UO₂)₂(SeO₄)₄(H₂O)₂](H₂O)₅ (2) were prepared by isothermal evaporation at room temperature. The crystal structure of 1 was solved by the direct method [C2/c, a = 17.879(5), b = 8.152(5), c = 17.872(5) Å, β = 96.943(5)°, V = 2585.7(19) ų, Z = 4] and refined to R ₁ = 0.0449 (wR ₂ = 0.0952) for 2600 reflections with |F _o| ≥ 4σ _F . The structure of 2 was solved by the direct method [P2₁/c, a = 17.8377(5), b = 8.1478(5), c = 23.696(1) Å, β = 131.622(2)°, V = 2574.5(2) ų, Z = 4] and refined to R ₁ = 0.0516 (wR ₂ = 0.1233) for 4075 reflections with |F _o| ≥ 4σ _F . The structures of 1 and 2 are based on [(UO₂)₂(SeO₄)₄(H₂O)₂]^4? layers. The charge of the inorganic layer is compensated by potassium and oxonium ions arranged in the interlayer space. Each K ion is surrounded by seven O atoms belonging to uranyl selenate layers and water molecules, so that it binds with each other the adjacent uranyl selenate structural elements.     

Seebeck coefficient of V2O5-R2O3-TeO2 (R = Sb or Bi) glasses

The thermoelectric power of glasses in the systems V₂O₅-Sb₂O₃-TeO₂ and V₂O₅-Bi₂O₃-TeO₂ was measured at temperatures in the range 373–473 K. The glasses in both systems were found to be n-type semiconductors. The Seebeck coefficient, Q, at 473 K was determined as –192 to –151 VK^–1 for V₂O₅-Sb₂O₃-TeO₂ glasses, and –391 to –202 VK^–1 for V₂O₅-Bi₂O₃-TeO₂ glasses. For these glasses in both systems, Heikes' formula was satisfied adequately for the relationship between Q and In [C _v/(1-C_v)] (C _v = V⁴⁺/V_total, C _v is the ratio of the concentration of reduced vanadium ions), and discussions confirmed small polaron hopping conduction of the glasses in both systems. Mackenzie's formula relating to Q and V⁵⁺/V⁴⁺ was also applicable to the glasses in both systems, and it was concluded that the dominant factor determining Q was C _v.     

Thermodynamics of AII(BVUO6)2·nH2O (AII is Ni or Cu, BV is P or As)

The standard enthalpies of formation of nickel and copper uranophosphates and uranoarsenates at T = 298.15 K were determined. The temperature dependence of the isobaric heat capacity of these compounds in the range from 80 to 300 K was measured. Based on the results obtained, the standard entropies and Gibbs functions of formation of the compounds were evaluated. The thermodynamic characteristics of synthesis and dissolution of the compounds were evaluated.     

Electrical properties of nanocrystalline Ce(0.8)Sm(0.2)O(2-delta) and Ce(1-x)Gd(x)O(2-delta) (0.1 < or = x < or = 0.3) ceramics for IT-SOFC

Ce(0.8)Sm(0.2)O(2-delta) and Ce(1-x)Gd(x)O(2-delta) (0.1 < or = x < or = 0.3) nano-sized powders were successfully synthesized by the solution combustion synthesis process. The calcined nanopowders showed a ceria-based single phase with a cubic fluorite structure. In this study, we discussed the structural and electrical characteristics of the sintered Ce(0.8)Sm(0.2)O(2-delta) and Ce(1-x)Gd(x)O(2-delta). We obtained high-quality Ce(0.8)Sm(0.2)O(2-delta) and Ce(1-x)Gd(x)O(2-delta) ceramics with a high density, ultra-fine grain size, and high electrical conductivity even at low sintering temperature using the nanosized powders. The electrical conductivities at 800 degrees C for the Ce(0.8)Sm(0.2)O(2-delta) sintered at 1400 degrees C and the Ce(0.8)Gd(0.2)O(2-delta) sintered at 1350 degrees C were 0.110 and 0.104 Scm(-1), respectively.     

Mechanochemical transformation of mixtures of Ca(OH)2 and (NH4)2HPO4 or P2O5

A detailed comparative study of the mechanochemical transformation of two mixtures: Ca(OH)₂–(NH₄)₂HPO₄ and Ca(OH)₂–P₂O₅, milled in a mortar dry grinder for different periods of time was carried out. The phase transformations obtained at each milling stage were studied by X-ray diffraction, infrared spectroscopy, transmission electron microscopy, differential scanning calorimetry and thermogravimetric analysis.The transformations taking place during the first periods of milling are very different for both mixtures. However, prolonged milling, over nearly the same period, causes amorphization of both mixtures. DSC analysis of the milled powders showed the temperature of crystallization of hydroxyapatite and tricalcium phosphate (β-TCP). Calcinations of all the different milled powders at 800 °C for 2 h, results in the formation of hydroxyapatite and β-TCP.     

Third-order nonlinear optical properties of sol-gel-derived V(2)O(5), Nb(2)O(5), and Ta(2)O(5) thin films

The third-order nonlinear optical properties of sol-gel-derived V(2)O(5), Nb(2)O(5), and Ta(2)O(5) thin films have been investigated by the third-harmonic-generation method, and the effect of the metal-oxygen bond length on the third-order nonlinear optical susceptibility χ((3)) has been examined. The χ((3)) values of V(2)O(5), Nb(2)O(5), and Ta(2)O(5) thin films were 1.1 × 10(-11), 1.3 × 10(-12), and 6.1 × 10(-13) esu, respectively, which corresponds to an increase in the average bond length I(b) of the order of V-O (I(b) = 0.183 nm), Nb-O (I(b) = 0.200 nm), and Ta-O (I(b) = 0.204 nm). The current and previous results indicate that χ((3)) of these transition metal oxides with the empty d orbitals is dominated mainly by the metal-oxygen bond length rather than the valence of the metal cation. It is predicted on the basis of Lines' model that transition metal oxides with the shortest I(b) exhibit the highest χ((3)), whereas nontransition metal oxides with the longest I(b) exhibit the highest χ((3)).     

Dumbbell-like PtPd-Fe(3)O(4) Nanoparticles for Enhanced Electrochemical Detection of H(2)O(2)

Dumbbell-like Pt(x)Pd(100-x)-Fe(3)O(4) nanoparticles (NPs) were synthesized and studied for electrocatalytic reduction and sensing of H(2)O(2). In 0.1 M phosphate buffered saline (PBS) solution, the 4-10 nm Pt(x)Pd(100-x)-Fe(3)O(4) NPs showed the Pt/Pd composition-dependent catalysis with Pt(48)Pd(52)-Fe(3)O(4) NPs having the best activity. The Pt(48)Pd(52)-Fe(3)O(4) NPs were tested for H(2)O(2) detection, and their H(2)O(2) detection limit reached 5 nM, which was suitable for monitoring H(2)O(2) generated from Raw 264.7 cells. These dumbbell-like PtPd-Fe(3)O(4) NPs are the most sensitive probe ever reported and can be used to achieve real-time quantitative detection of H(2)O(2) in biological environment for biological and biomedical applications.     

Acousto-optic interaction in alpha-BaB(2)O(4)and Li(2)B(4)O(7) crystals

Experimental studies and analysis of acousto-optic diffraction in alpha-BaB(2)O(4) and Li(2)B(4)O(7) crystals are given. Ultrasonic wave velocity, elastic compliance and stiffness coefficients, and piezo-optic and photoelastic coefficients of alpha-BaB(2)O(4) and Li(2)B(4)O(7) crystals are determined. The acousto-optic figure of merit has been estimated for different possible geometries of acousto-optic interaction. It is shown that the acousto-optic figures of merit for alpha-BaB(2)O(4) crystals reach the value M(2)=(270 +/- 70) x 10(-15) s(3)/kg for the case of interaction with the slowest ultrasonic wave. The directions of propagation and polarization of those acoustic waves are obtained on the basis of construction of acoustic slowness surfaces. The acousto-optic diffraction is experimentally studied for alpha-BaB(2)O(4) and Li(2)B(4)O(7) crystals.     

(Ba(x)La(1-x)(2))In(2)O(5+x) (0.4 < or = x < or = 0.6) electrolyte-supported mixed-potential CO sensors

The dense (Ba(x)La(1-x)(2))In(2)O(5+x) electrolytes with different compositions (x = 0.4, 0.5, 0.6) were synthesized by Pechini method. The obtained sintered (Ba(x)La(1-x)(2))In(2)O(5+x) electrolytes showed a high relative density of approximately 98%, and the major phase of three electrolyte compositions was indexed as a cubic phase. The CO sensing properties of as-fabricated planar-type (Ba(x)La(1-x)(2))In(2)O(5+x)-based sensors coupled with ITO and Pt as the sensing electrode and reference electrode, respectively, were investigated. The effects of factors such as gas flow rate, chemical compositions, and density of the electrolytes on the sensing performance were investigated. The sensors showed good sensitivity to different concentrations of CO from approximately 100 to approximately 500 ppm and excellent selectivity over low concentrations of methane (<500 ppm). Linear relationships between emf of the sensors and CO gas concentrations from approximately 100 to approximately 400 ppm were observed. However, the sensors indicated more sluggish response compared with the sensors coupled with a corresponding porous electrolyte. The probable reason has been discussed. The long-term stability of the sensor for the detection of CO was also investigated, which indicated a reasonably stable sensor signal after an initial decline during the incubation period.     

Combustion Synthesis of Glass (B2O3-Al2O3-MgO)-Ceramic (TiB2) Composites

The combustion synthesis, or self-propagating high temperature synthesis (SHS), technique has been used to produce glass ceramic composites that have a glass matrix based on B₂O₃-MgO-Al₂O₃and a crystalline ceramic phase of TiB₂. Conditions for producing glassy materials by the SHS technique are discussed and the thermodynamics of these combustion reactions are analyzed. The combustion characteristics, i.e., ignition energy, combustion temperature, and wave velocity have been determined. Green density of the pellets had a significant effect on the combustion characteristics. Green pellets with low density were used to reduce heat loss, thus enabling the synthesis of those compositions having low adiabatic temperatures. The glass-forming region of these SHS glasses was found to be in relatively good agreement with that of samples produced by the traditional furnace-melting method.     

Electrical conductivity of (ZrO2)0.85(CeO2)0.12 (Y2O3)0.03

A number of zirconia-based materials show promise as electrode materials in magnetohydrodynamic (MHD) generators. As a part of an exploratory programme to find suitable materials for graded electrode applications in MHD generators, partially stabilized and fully stabilized sintered ceramic materials are prepared and characterized. The oxygen ion transference number t _ion(O^2–) and electrical conductivity of this material are measured up to 1670 K in the oxygen partial pressure range 1 to 10^–6 atm. The activation energies for conduction are determined. The electrical properties of this material are characterized by mixed conduction, ionic and electronic. The observed conductivity data are explained in terms of the defect equilibrium reactions between tetravelent Ce⁴⁺ and trivalent Ce³⁺ ions.     

Proton Conductivity of Cs2MnH3(P2O7)2 and Rb2MnHP2O7(H2PO4)2

Cs₂MnH₃(P₂O₇)₂ and Rb₂MnHP₂O₇(H₂PO₄)₂ are shown to have an appreciable proton conductivity: 5 × 10^–8 and 2 × 10^–5 S/cm in the Cs compound at 298 and 400 K, respectively, and 10^–7 and 4 × 10^–7 S/cm in the Rb compound. The conductivity and structural data are analyzed in relation to the mechanisms of protonic conduction in these mixed phosphates.     

Prussian blue based nanoelectrode arrays for H(2)O(2) detection

We propose to form nanoelectrode arrays by deposition of the electrocatalyst through lyotropic liquid crystalline templates onto inert electrode support. Whereas Prussian Blue is known to be a superior electrocatalyst in hydrogen peroxide reduction, carbon materials used as electrode support demonstrate only a minor activity. We report on the possibility for nanostructuring of Prussian Blue by its electrochemical deposition through lyotropic liquid crystalline templates, which is noticed from atomic force microscopy images of the resulting surfaces. The resulting Prussian Blue based nanoelectrode arrays in flow injection analysis mode demonstrate a sub-part-per-billion detection limit (1 x 10(-)(8) M) and a linear calibration range starting exactly from the detection limit and extending over 6 orders of magnitude of H(2)O(2) concentrations (1 x 10(-)(8) to 1 x 10(-)(2) M), which are the most advantageous analytical performances in hydrogen peroxide electroanalysis.     

Carbon nanotube-TiO(2) hybrid films for detecting traces of O(2)

Hybrid titania films have been prepared using an adapted sol-gel method for obtaining well-dispersed hydrogen plasma-treated multiwall carbon nanotubes in either pure titania or Nb-doped titania. The drop-coating method has been used to fabricate resistive oxygen sensors based on titania or on titania and carbon nanotube hybrids. Morphology and composition studies have revealed that the dispersion of low amounts of carbon nanotubes within the titania matrix does not significantly alter its crystallization behaviour. The gas sensitivity studies performed on the different samples have shown that the hybrid layers based on titania and carbon nanotubes possess an unprecedented responsiveness towards oxygen (i.e.?more than four times higher than that shown by optimized Nb-doped TiO(2) films). Furthermore, hybrid sensors containing carbon nanotubes respond at significantly lower operating temperatures than their non-hybrid counterparts. These new hybrid sensors show a strong potential for monitoring traces of oxygen (i.e.?≤10?ppm) in a flow of CO(2), which is of interest for the beverage industry.     

Mechanochemical synthesis of hydroxyapatite from Ca(OH)2-P2O5 and CaO-Ca(OH)2-P2O5 mixtures

Dry grinding of Ca(OH)₂-P₂O₅ and CaO-Ca(OH)₂-P₂O₅ mixtures was conducted by a planetary ball mill to investigate the mechanochemical solid-phase reaction for the synthesis of hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂, HAp). HAp was synthesized by grinding of the two sets of mixtures. The formation of HAp from the Ca(OH)₂-P₂O₅ mixture was more advantageous than that from the CaO-Ca(OH)₂-P₂O₅ one. This synthesis reaction from the former mixture was almost completed within 30 min of grinding. The presence and amount of H₂O contained in the starting mixtures played a key role to promote the formation of HAp. Especially, in the former mixture, the prolonged grinding assisted the solid-phase reaction of the intermediate DCPD and Ca(OH)₂ to produce HAp more effectively.     

Aluminium based composites strengthened with metallic amorphous phase or ceramic (Al2O3) particles

Two methods were used to obtain amorphous aluminium alloy powder: gas atomization and melt spinning. The sprayed powder contained only a small amount of the amorphous phase and therefore bulk composites were prepared by hot pressing of aluminium powder with the 10% addition of ball milled melt spun ribbons of the Al₈₄Ni₆V₅Zr₅ alloy (numbers indicate at.%). The properties were compared with those of a composite containing a 10% addition of Al₂O₃ ceramic particles. Additionally, a composite based on 2618A Al alloy was prepared with the addition of the Al₈₄Ni₆V₅Zr₅ powder from the ribbons used as the strengthening phase. X-ray studies confirmed the presence of the amorphous phase with a small amount of aluminium solid solution in the melt spun ribbons. Differential Scanning Calorimetry (DSC) studies showed the start of the crystallization process of the amorphous ribbons at 437 °C. The composite samples were obtained in the process of uniaxial hot pressing in a vacuum at 380 °C, below the crystallization temperature of the amorphous phase. A uniform distribution of both metallic and ceramic strengthening phases was observed in the composites. The hardness of all the prepared composites was comparable and amounted to approximately 50 HV for those with the Al matrix and 120 HV for the ones with the 2618A alloy matrix. The composites showed a higher yield stress than the hot pressed aluminium or 2618A alloy. Scanning Electron Microscopy (SEM) studies after compression tests revealed that the propagation of cracks in the composites strengthened with the amorphous phase shows a different character than these with ceramic particles. In the composite strengthened with the Al₂O₃ particles cracks have the tendency to propagate at the interfaces of Al/ceramic particles more often than at the amorphous/Al interfaces.     

H(2)O(2)-generating peroxidase electrodes as reagentless cyanide sensors

Inexpensive, reagentless, and simple (single-electrode) cyanide biosensors are developed using a pyrolytic graphite (PG) electrode on which horseradish peroxidase (HRP) is adsorbed. The electrode is poised at -300 mV vs Ag/AgCl for 40 s to reduce dissolved O(2) to H(2)O(2) at the PG surface. The generated H(2)O(2) accumulates in the diffusion layer. The potential is then stepped to 0 mV, at which the accumulated H(2)O(2) is reduced, though the O(2) reduction does not proceed. Since the H(2)O(2) reduction is catalyzed by HRP, the transient cathodic current is inhibited by cyanide. Therefore, the transient current is a function of the cyanide concentration. A HRP/PG electrode with saturated HRP coverage is reliable, and it can determine 10(-)(5)-10(-)(3) M cyanide. On the other hand, the electrode with lower HRP coverage is less reliable, though it is so sensitive as to detect 2 × 10(-)(7) M cyanide because the system is under kinetic control.     

Preparation and characterization of Ti/SnO(2)-Sb(2)O(3)-Nb(2)O(5)/PbO(2) thin film as electrode material for the degradation of phenol

In this work, a novel electrode of titanium substrate coated with mixed metal oxides of SnO(2), Sb(2)O(3), Nb(2)O(5) and PbO(2) was successfully prepared using thermal decomposition and electrodeposition. The surface morphology and the structure of the prepared thin film were characterized by scanning electronic microscopy (SEM) and X-ray diffraction (XRD), respectively. Experimental results showed that the structure of the prepared electrode might be described as a Ti/SnO(2)-Sb(2)O(3)-Nb(2)O(5)/PbO(2) thin film and its surface was mainly comprised pyramidal-shape beta-PbO(2) crystals. The modified electrode had higher oxygen evolution potential than that of other PbO(2) modified electrodes. Electrocatalytic oxidation of phenol in aqueous solution was studied to evaluate the potential applications of this electrode in environmental science. The phenol removal efficiency in an artificial wastewater containing 0.50g/L phenol could reach 78.6% at 20 degrees C and pH 7.0 with an applied electricity density of 20mA/cm(2) and treatment time of 120min. When 21.3g/L chloride was added to this wastewater, the removal efficiency could reach to 97.2%.     

Synthesis and microstructural characterization of Ce1-xTb(x)O2-delta (0 < or = x < or = 1) nano-powders

Ce1-xTb(x)O2-delta nano-powders have been successfully synthesized by using the ammonium carbonate coprecipitation method in an entire compositional range of 0 < or = x < or = 1 by adjusting the preparation conditions. Studies of X-ray diffraction (XRD) and transmission electron microscopy (TEM) showed that the powders with different compositions mainly consist of fluorite structure. In addition, a small amount of secondary phase was observed in the powders with x > or = 0.7. TEM observation indicated that the secondary phase could have a superstructure formed by a structural modulation of the fluorite structure.