Studies on Indian Ocean Manganese Nodules: XI. Physicochemical Characterization and Catalytic Activity of Silver Oxide Mixed Manganese Nodules

The promoting effect of Ag₂O on the physicochemical properties and catalytic activity of manganese nodules has been investigated. The surface area and surface oxygen increased with addition of Ag₂O, reaching a maximum at 1 mol% of Ag, and then decreased with further addition of Ag₂O. The catalytic activity of manganese nodules substantially increased with addition of Ag₂O over a wide range (0.25–25 mol% Ag). Addition of only 0.25 mol% of Ag to the nodule decreased the temperature of complete CO oxidation from 350°C to as low as 100°C. This enhanced activity was explained by the concerted action of Ag and Mn, where CO was preferentially adsorbed on Ag₂O and oxidized. The reduced Ag was then reoxidized rapidly by oxygen transferred from Mn. The promoting effect of Ag₂O on H₂O₂decomposition and ketonization of acetic acid, however, was less pronounced.     

A new ferroelectric oxide Li2Pb2Pr2W2Ti4Nb4O30: Synthesis and characterization

A new ferroelectric oxide (Li₂Pb₂Pr₂W₂Ti₄Nb₄O₃₀) of tungsten bronze structural family has been synthesized by a solid-state reaction (mixed-oxide) route at high temperature (～1100 °C). X-ray structural analysis with room temperature diffraction data confirms the formation of a single phase compound. The scanning electron microscopic (SEM) texture of the surface of material sample exhibits a uniform grain distribution with a few small voids suggesting the formation of high-density pellet sample. Detailed studies of dielectric constant, tangent loss and polarization with temperature and frequency confirmed the existence of ferroelectric properties in the material with transition temperature much above room temperature. Study of electrical properties (impedance, modulus, conductivity, etc.) of the material exhibits a strong correlation between its micro-structure (i.e., bulk, grain boundary, etc.) and electrical parameters. The nature of variation of dc conductivity with temperature confirms the Arrhenius behavior of the material. The presence of ionic conductivity in the material was observed in its ac conductivity spectrum. Study of frequency dependence of ac conductivity suggests that the material obeys Jonscher's universal power law. The experimental electrical transport properties of the material clearly exhibit the existence of non-exponential-type of conductivity relaxation.     

三种特殊的双固定步网络环的生成树的数目

令Ｔ（Ｃ＾－（ｎ，ｌ，ｐ）是双固定步网络环Ｃ＾－（ｎ，ｌ，ｐ）的生成树的数目，在本文中给出了关于Ｔ（Ｃ＾－（ｎ，１，２）），Ｔ（Ｃ＾－（ｎ，１，３）和Ｔ（Ｃ＾－（ｎ，１，４））的三种递推式，且一般情况，Ｔ（Ｃ＾－（ｎ，１，ｐ）也可以按此思想考虑。     

Solid-state synthesis and heat capacity measurements of ceramic compounds LiAlSiO4, LiAlSi2O6, LiAlSi3O8, and LiAlSi4O10

Number of lithium-based oxide ceramics in Li–Al–Si–O system were synthesized by solid-state reaction route using Li₂CO₃, Al₂O₃, and SiO₂. The progress of the reaction was monitored using thermogravimetry. A model-free approach was employed to fit the temperature versus mass loss data. Heat capacities were measured as a function of temperature using differential scanning calorimetry. Variation of lithium/silicon ratio resulted in change in heat capacity and average crystallite size in each compound.     

Calcined Mg-Fe-CO(3) LDH as an adsorbent for the removal of selenite

Mg-Fe-CO(3) layered double hydroxide (LDH) with a Mg/Fe molar ratio of 2.0 was synthesized by co-precipitation method and its calcined product (CLDH) was obtained by heating Mg/Fe-LDH at 500 degrees C. Sorption of SeO(2-)(3) on CLDHs was studied and the results indicate that the sorption capacity of CLDHs was higher than that of uncalcined LDHs. Isotherms for SeO(2-)(3) sorption by CLDHs were well described using the Freundlich and Langmuir equations. The thermodynamic parameters, viz. DeltaG*, DeltaH*, DeltaS* were calculated to predict the nature of adsorption. The negative and positive values of DeltaG* and DeltaH* indicate that the adsorption process is spontaneous and endothermic in nature, respectively. The adsorption process followed first-order kinetics.     

Regularized numerical integration of multibody dynamics with the generalized method

This paper discusses the consistent regularization property of the generalized α method when applied as an integrator to an initial value high index and singular differential-algebraic equation model of a multibody system. The regularization comes from within the discretization itself and the discretization remains consistent over the range of values the regularization parameter may take. The regularization involves increase of the smallest singular values of the ill-conditioned Jacobian of the discretization and is different from Baumgarte and similar techniques which tend to be inconsistent for poor choice of regularization parameter. This regularization also helps where pre-conditioning the Jacobian by scaling is of limited effect, for example, when the scleronomic constraints contain multiple closed loops or singular configuration or when high index path constraints are present. The feed-forward control in Kane’s equation models is additionally considered in the numerical examples to illustrate the effect of regularization. The discretization presented in this work is adopted to the first order DAE system (unlike the original method which is intended for second order systems) for its A-stability and same order of accuracy for positions and velocities.     

Ferroelectric and optical properties of ‘Ba-doped’ new double perovskites

Solid solution of Pb_1.5Ba_0.5BiNbO₆ ceramic is explored here to obtain its ferroelectric and optical properties. The polycrystalline sample was prepared by a standard solid state reaction route. Room temperature XRD and FTIR spectra of the compound exhibit an appreciable change in its crystal structure of Pb₂BiNbO₆ on addition of ‘Ba’ in A site. The surface morphology of the gold-plated sintered pellet sample recorded by SEM exhibits a uniform distribution of small grains with well-defined grain boundaries. Detailed studies on the nature of polarization and variation of dielectric constant, tangent loss with temperature as well as frequency indicate the existence of Ferro-electricity in the sample. Using UV-Vis spectroscopy, the optical band gap of the studied sample has been estimated as 2.1 eV, which is useful for photo catalytic devices. Photoluminescence analysis of the powder sample shows a strong red photoluminescence with blue excitation, which is basically useful for LED.     

Importance of specific surface area and basic sites of the catalyst in oxidative coupling of CH4 over LiO/MgO catalysts prepared by precipitation methods

A low specific surface area was found to be the key factor for catalytic conversion of CH₄ into C₂H₆ and C₂H₄. C₂-hydrocarbon selectivity increases with increase in basicity of the catalyst.

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CH₄ C₂H₆ C₂H₄. C₂- .