New uniform solid catalyst for the low-temperature oxidation of carbon monoxide: A triple-layered rare earth perovskite containing Co and Cu ions

Oxygen reactivity and catalytic activity of the cobalt-containing layered defect perovskites, YBa2Cu2CoO7+delta and LaBa2Cu2CoO7+delta, in comparison with LaBa2Cu3O7-delta have been investigated employing temperature-programmed desorption (TPD) and temperature-programmed surface reactions (TPSR) in the stoichiometric and catalytic mode using carbon monoxide as a probe molecule. TPD studies showed evidence for the presence of two distinct labile oxygen species, one at (0 0 1/2) sites and the other at (0 1/2 0) sites in LaBa2Cu2CoO7+delta against a single labile species at (0 1/2 0) in the case of two other oxides. The activation energies for the catalytic oxidation of carbon monoxide by oxygen over LaBa2Cu3O7-delta, YBa2Cu2CoO7+delta, and LaBa2Cu2CoO7+delta have been estimated to be 24.2, 15.9, and 13.6 kcal/mol, respectively. The reactivity and catalytic activity of the oxide systems have been interpreted in terms of the structural changes brought about by substituents, guided by a directing effect of the larger rare earth cation. TPSR profiles, structural analysis, and infrared spectroscopic investigations suggest that the oxygen present at (0 0 1/2) sites in the case of LaBa2Cu2CoO7+delta is accessible to catalytic oxidation of CO through a Mars-Van Krevelen pathway. Catalytic conversion of CO to CO2 over LaBa2Cu2CoO7+delta occurs at 200 degrees C. The enhanced reactivity is explained in terms of changes brought about in the coordination polyhedra around transition metals, enhanced basal plane oxygen diffusivity, and redox potentials of the different transition metal cations.

Pyroelectric and Electrostrictive Properties of (1 –x–y) PZN ·xBT ·yPT Ceramic Solid Solutions

The pyroelectric and electrostrictive properties of lead zinc niobate-lead titanate-barium titanate (PZN-BT-PT) ceramic solid solution were investigated. These properties of the (1 - x)PZN.xBT series were qualitatively explained with a composition fluctuation model. The pyroelectric depolarization temperatures of (1 - x - y)PZN.xBT.yPT ceramics were utilized to select compositions for room-temperature electrostrictive applications. Among them, 0.85PZN.0.10BT.0.05PT ceramic with Q11 = 0.018 m4/C2, Q12 = -0.0085 m4/C2, S2 at 25 kV/cm = -6.1 x 10(-4), T(max) = 75-degrees-C at 1 kHz, and T(t) = 27-degrees-C shows optimum properties for micropositioner applications.

Realtime kinetic analysis of antigen-antibody interaction using solid phase binding: Transformation of hCG-monoclonal antibody complex

Kinetic constants of MAb-hCG interactions have been determined using solid phase binding of I-125[hCG] to immobilized MAb. While association has been shown to follow the expected pattern, dissociation consists of at least two reversible steps, one with a rate constant of 0.0025 min(-1), and a second with a rate constant of 0.00023 min(-1). Validity of affinity constant measurements in the light of the complex reaction kinetics is discussed, A comparison between the method of surface plasmon resonance technology (BIAcore) and solid phase binding (SPB) for determination of kinetic parameters shows that SPB provides not only a cost-effective approach for determination of realtime kinetic parameters of macromolecular ligand-ligate interaction but also a method with several advantages over the BIAcore system in investigating the mechanism of antigen-antibody interaction.

Studies in crystal engineering: Effect of fluorine substitution in crystal packing and topological photodimerization of styryl coumarins in the solid state

Styryl coumarins generally yield centrosymmetric (alpha-mode, anti-HT) photodimers when subjected to irradiation in the solid state, However, the substitution of fluorine dramatically alters the packing mode and steers the molecules 4-(4-fluorostyryl)coumarin 1 and 4-(2-fluorostyryl)coumarin 2 to form a stereospecific photodimer, beta-mode, syn-HH across the styrenic double bond (yield 78-85%). The stereochemistry of the photodimer 2a has been established by X-ray crystallography. There is no evidence for the presence of C-H ... F interactions. The true nature of the weak atom-atom interactions called into play when fluorine is substituted is not clear, It is observed that the fluoro substituted compounds have greater crystal density than the corresponding unsubstituted ones.

Solid state amorphization in binary Ti---Ni, Ti---Cu and ternary Ti---Ni---Cu system by mechanical alloying

An amorphous phase has been synthesized by mechanical alloying in a planetary mill over a nickel content range of 10�70 at.% in the Ti---Ni system and a copper content range of 10�50 at.% in the Ti---Cu system. In the case of ternary Ti---Ni---Cu alloys the glass-forming composition range has been found to be given by x = 10�20 for Ti60Ni40 ? xCux, x = 10 � 30 for Ti50Ni50 ? xCux and x = 10 � 40 for Ti40Ni60 ? xCux alloys. The difficulty in the amorphization of copper-rich compositions is explained in the light of enthalpy composition diagrams calculated for the ternary solid solution and the amorphous phase.

Solid-state photobehaviour and crystal packing of o-chlorobenzylidene-DL-piperitone: influence of molecular topology on photobehaviour

C17H19ClO, M(r) = 274.7, triclinic, P1BAR, a = 11.154 (3), b = 12.685 (2), c = 12.713 (2) angstrom, alpha = 100.68 (1), beta = 113.58 (1), gamma = 104.50 (2)-degrees, V = 1511.1 (6) angstrom3, Z = 4, D(m) = 1.22, D(x) = 1.215 Mg m-3, Cu K-alpha, lambda = 1.5418 angstrom, mu = 2.16 mm-1, F(000) = 584, T = 293 K, R = 0.057 for 3481 observed reflections. The title compound is photostable in the crystalline state and lattice-energy calculations have been employed to rationalize the photobehaviour. The well-known beta-steering ability of the chloro group is not operative in this system as there are no Cl...Cl interactions in the crystal lattice. All five benzylidene-DL-piperitone structures so far studied are alpha-packed and the molecular topology appears to be a deciding factor even in the presence of steering groups.

Structural and vibrational studies of the layered structure solid Fe1 ? xNixPS3 (1 greater-or-equal, slanted x greater-or-equal, slanted 0)

We report here the results of structural and vibrational studies on the solid solution Fe1 ? xNixPS3 (1 greater-or-equal, slanted x greater-or-equal, slanted 0) systems. From the structural analysis, we show that there is a lattice compaction as the composition x is varied from 0 to 1, the basic lattice symmetry being maintained. We find that the compaction is more in the basal plane. These subtle structural changes are also reflected in the vibrational bands. We observed splitting of certain bands due to these small changes in the lattice constants, which we explained as arising from a correlation splitting. These changes in the vibrational bands have also been seen on cooling where there is a preferential thermal compaction in the basal plane compared to that perpendicular to the plane.

Evaluation of relative growth limitation due to depletion of glucose and oxygen during fungal growth on a spherical solid particle

A mathematical model for glucose and oxygen consumption, and cell growth during fungal growth on a single solid particle is developed. A moving biofilm is assumed to be present on the surface of the solid particle. Initially only glucose is assumed to be growth limiting and later oxygen transferred from the gas phase on to the biofilm is also assumed to be growth limiting. Glucose is found to be severely growth limiting when assumed to be the only growth limiting factor and its limiting levels far less severe when oxygen limitation is also included. The objective of the model is to gain a better understanding of the mass transfer and relative growth limiting characteristics of glucose and oxygen in fungal growth systems. The results obtained from the model proposed here will be the subject of future work.

Phase Relations in the System La-Rh-O and Thermodynamic Properties of LaRhO3

Phase relations in the system La-Rh-O at 1223 Ii have been determined by examination of equilibrated samples by optical and scanning electron microscopy, powder X-ray diffraction (XRD), and energy-dispersive analysis of X-rays (EDAX). Only one ternary oxide, LaRhO3, with distorted orthorhombic perovskite structure (Pbnm, a = 0.5525, b = 0.5680, and c = 0.7901 nm) was identified. The alloys and intermetallics along the La-Rh binary are in equilibrium with La2O3. The thermodynamic properties of LaRhO3 were determined in the temperature range 890 to 1310 K, using a solid-state cell incorporating yttria-stabilized zirconia as the electrolyte. A new four-compartment design of the emf cell was used to enhance the accuracy of measurement. For the reaction 1/2La(2)O(3) + 1/2Rh(2)O(3) --> LaRhO3, Delta G degrees = - 70 780 + 4.89T (+/- 90) J.mol(-1) The compound decomposes on heating to a mixture of La2O3, Ph and O-2. The calculated decomposition temperatures are 1843 (+/- 5) K in pure O-2 and 1728 (+/- 5) K in air at a pressure of 1.01 x 10(5) Pa. The phase diagrams for the system La-Rh-O at different partial pressures of oxygen are calculated from the thermodynamic information.

Solid Oxide-Ion Electrolytes

Solid oxide-ion electrolytes find application in oxygen sensors, oxygen pumps and in high-temperature electrolyser-fuel-cell hybrid systems. All the solid electrolytes known so Qr, however, exhibit: tow oxide-ion conductivities below 973 K. Therefore, there is a need for fast oxide-ion conductors operative at temperatures around 673 K, Recently, efforts have been directed towards developing such materials. This article summarizes various type of oxide-ton electrolytes reported in literature and outlines a strategy for the identificatiom/synthesis of improved materials.

Solid-state miscibility gap and thermodynamics of the system BaO–SrO

A solid-state miscibility gap in the pseudo-binary system BaO-SrO is delineated by X-ray diffraction studies on samples equilibrated either in vacuum or under flowing inert gas at temperatures between 1073 and 1423 K. For the SrxBa1-xO solid solution an asymmetric phase boundary, characterized by a critical temperature of 1356 (+/-4) K and composition x=0.55 (+/-0.008), is obtained. Thermodynamic mixing properties of the solid solution, derived from the experimental phase boundary compositions and temperatures, can be represented by the expression: Delta G(E)=x(1-x){33 390-7.09T)x+(29 340-6.23T)(1-x)} J mol(-1)It is necessary to include excess entropy terms to obtain a good fit to the experimental data. The chemical spinodal curve is computed from the thermodynamic parameters

Some observations on the ignition of composite solid propellants

Heat-up times derived from studies on the ignition characteristics of a few model composite solid propellants, containing polystyrene, carboxy-terminated polybutadiene, plasticised polyvinyl chloride and polyphenol formaldehyde as binders, show that they are directly proportional to the mass of the sample and inversely proportional to the hear flux. Propellant weight-loss prior to ignition and high pressure ignition temperature data on the propellants, ammonium per chlorate, and binders show that the ignition is governed by the gasification of the binder pyrolysis products. The activation energy for the gasification of the pyrolysed polymer products corresponds to their ignition behaviour suggesting that propellant ignition is controlled by the binder.

Structural and Dielectric-Properties Of A Novel BI2O3-(1-X)WO3-XCUO Solid-Solution

A novel solid solution in the system Bi-W-Cu-O has been synthesized and its structural and dielectric properties studied. The solid solution Bi2O3-(1-x)WO3-xCuO exists up to x = 0.7; the solid solutions up to x = 0.65 are orthorhombic but stabilize in tetragonal structure in a narrow range around x = 0.7. The solid solutions are non-centrosymmetric and exhibit ferroelectric behaviour similar to their parent phase Bi2WO6. The Curie point of the solid solution is found to decrease with increase in x.

Activities in the spinel solid solution FeXMg1−XAl2O4

Abstract: Activities in the spinel solid solution FexMg1-xAl2O4 saturated with alpha-Al2O3 have been measured for the compositional range 0 < X < 1 between 1100 and 1350 K using a bielectrolyte solid-state galvanic cell, which may be represented as Pt, Fe + FexMg1-xAl2O4 + alpha-Al2O3//(Y2O3)ThO2/ (CaO)ZrO2//Fe + FeAl2O4 + alpha-Al2O3, Pt Activities of ferrous and magnesium aluminates exhibit small negative deviations from Raoult's law. The excess free energy of mixing of the solid solution is a symmetric function of composition and is independent of temperature: Delta G(E) = -1990 X(1 - X J/mol. Theoretical analysis of cation distribution in spinel solid solution also suggests mild negative deviations from ideality. The lattice parameter varies linearly with composition in samples quenched from 1300 K. Phase relations in the FeO-MgO-Al2O3 system at 1300 K are deduced from the results of this study and auxiliary thermodynamic data from the literature. The calculation demonstrates the influence of intracrystalline ion exchange equilibrium between nonequivalent crystallographic sites in the spinel structure on intercrystalline ion exchange equilibrium between the monoxide and spinel solid solutions (tie-lines). The composition dependence of oxygen partial pressure at 1300 K is evaluated for three-phase equilibria involving the solid solutions Fe + FexMg1-xAl2O4 + alpha-Al2O3 and Fe + FeyMg1-yO + FexMg1-xAl2O4. Dependence of X, denoting the composition of the spinel solid solution, on parameter Y, characterizing the composition of the monoxide solid solution with rock salt structure, in phase fields involving the two solid solutions is elucidated. The tie-lines are slightly skewed toward the MgAl2O4 corner.

Combustion synthesis and properties of nanostructured ceria-zirconia solid solutions

Nanostructured ceria-zirconia solid solutions (Ce1 − xZrxO2, X = 0 to 0.9) have been synthesized by a single step solution combustion process using cerous nitrate, zirconyl nitrate and oxalyl dihydrazide (ODH) / carbohydrazide (CH). The as-synthesized powders show extensive XRD line broadening and the crystallite sizes calculated from the XRD line broadening are in the nanometer range (6–11 nm). The combustion derived ceria zirconia solid solutions have high surface area in the range of 36–120 m2/g. Calcination of Ce1 −xZrxO2 at 1350 °C showed three distinct solid solution regions: single phase cubic (x ≤ 0.2), biphasic cubic-tetragonal (0.2 < x Image .8) and tetragonal (x > 0.8). When x ≥ 0.9, the metastable tetragonal phase formed transforms to monoclinic phase on cooling after calcination above 1100 °C. The homogeneity of Ce1 − xZrxO2 has been confirmed by EDAX analysis. The Temperature Programmed Reduction (TPR) measurement of Ce0.5Zr0.5O2 was carried out with H2 and the TPR profile showed two water formation peaks corresponding to the utilization of surface and bulk oxygen.