Degree Of Chemical Interaction Research Articles

Ni/CeO2 catalysts for methane partial oxidation: Synthesis driven structural and catalytic effects

Catalytic partial oxidation of methane (CPO) to synthesis gas was performed over differently prepared CeO2 supported nickel catalysts with 6wt% Ni content. The samples were synthesized by microwave assisted procedures and by hydrothermal deposition procedure. Differences in the catalyst structural properties of the prepared catalysts were detected by XRD, TPR and XPS measurement. When tested at atmospheric pressure with feed gas mixture containing methane and oxygen in molecular ratio CH4/O2=2, all the samples reached 98% conversion with CO selectivity values >95% in the 700–800°C temperature range. The samples exhibited different behavior towards carbon formation during the tests. Moreover, according to XRD, XPS and TGA results, when the carbon was formed it did not cause catalyst deactivation. TPR profiles confirmed different degree of chemical interaction between NiO and CeO2 support, depending on the preparation method. The building up or the easy removal of carbon during the CH4 temperature programmed surface reaction (TPSR), substantiate the role of the CeO2 lattice oxygen mobility, enhanced by metal-support interaction, in the removal of the deposited carbon through CO evolution. Structure-activity relationship established a close dependence of the CPO performance on the combination of NiO and CeO2 crystallite sizes and the interaction between the two.

Continuous C fibre composites with a porous ZrB2 Matrix

Abstract ZrB 2 –continuous C fibre composites were prepared by vacuum-bag infiltration and hot pressing, using 1D fabric carbon preforms from different commercial products. Sintering behaviour and microstructural features such as secondary phases and matrix/fibre interface were analysed. The infiltration process allowed the overall fibre content to be increased up to 70 vol.%, whilst the matrix densification was enabled by sintering aids. Due to presence of residual porosity, the degree of chemical interaction at the fibre/matrix interface was limited and this resulted in an easier pull out in the fractured surfaces, even in absence of fibre protective coating. The composites exhibited a damage tolerant behaviour.

From random chopped to oriented continuous SiC fibers–ZrB2 composites

ZrB2–continuous SiC fiber composites were prepared by vacuum-bag infiltration and hot pressing, using homemade 1D fabric preforms of Tyranno SA3 SiC fibers. Sintering behavior and microstructural features such as secondary phases and matrix/fiber interface were compared to those of chopped SiC fibers-reinforced composites. The infiltration process allowed the overall fiber content to be increased up to 40vol%, because of the ordered arrangement of fibers. When the fiber preforms were properly infiltrated, the composites were nearly fully dense and the densification mechanisms were the same as those of unreinforced matrices. Different from composites containing short discontinuous fibers, the degree of chemical interaction at the fiber/matrix interface was very limited and this resulted in an easier pull out in the fractured surfaces, even in absence of fiber protective coating.

Control of phase separation in blends of polyfluorene (co)polymers and the C 60-derivative PCBM

When creating thin films of polymer blends, interesting morphologies are formed because of phase separation. In particular for conjugated polymers, which are used as active material in optoelectronic devices, it is very important to understand the parameters that influence the phase separation process and to achieve control over the morphology. The overall goal of this blend morphology study is to contribute to the design of device structures with desired performance. Here we present results of morphology studies on thin films of polyfluorene-based blends with the fullerene derivative [6,6]-phenyl-C 61-butyric acid methyl ester (PCBM). The polymers used are poly(9,9-dioctylfluorene) (F8) and four different copolymers of F8. The thin films are spin coated from chloroform solutions onto silicon substrates and their surface morphology is imaged by tapping mode atomic force microscopy (AFM). We observe that the size and the shape of the domains in the film depend on the structure of the polymer. The nature of the monomer that, together with F8, is building the repeating unit in the copolymers has a strong effect on the phase separation in the polymer: PCBM blend. Since phase separation is influenced by interactions between components of the blend and the solvent, these results indicate that the degree of chemical interaction between polymer, solvent and PCBM, is different for the different blends. For the systems that form larger domains there is a clear correlation between the domain size (area) and the polymer/PCBM blend ratio. We also observe that the spin speed affects the thickness of the films and that the domain size increases with increasing thickness, primarily due to longer drying times.

The Discovery and Study of Nanocrystalline TiO2-(MoO3) Core−Shell Materials

Here we report the synthesis of a series of new nanocrystalline TiO2-(MoO3) core−shell materials whose photoabsorption energy (PE, the energy required to excite TiO2-core valence band electrons to MoO3-shell conduction band states) properties are correlated with both the nanoparticle size and the degree of chemical interaction between the TiO2 core and the MoO3 shell. The TiO2-(MoO3) nanoparticle size can be readily adjusted from 80 to 40 A, and in this series, the PE decreases from 2.88 to 2.60 eV with decreasing particle size. The systematic PE red-shift exhibited by the core−shell materials is ascribed to the change in the relative position of the MoO3-shell conduction band as it evolves from less than a monolayer to a two monolayer shell.

Interaction of Molten Salts with a Semianthracite Char at 873 K. A Study by X-ray Diffraction

The chemical changes produced as a result of the interaction of molten salts with mineral components of a semianthracite char (AC) at 873 K in N2 are investigated. AC samples were treated with the LiCl/KCl eutectic mixture. Generally, a metal oxide (CaO, MgO, FeO, CoO, NiO, Cu2O, or ZnO) was added to the alkali metal chlorides. After the treatments of AC, the residual solid mass was washed with distilled water and oven-dried. The resultant samples were analyzed by X-ray diffraction.The degree of chemical interaction with the inorganic fraction of AC depended on the composition of the molten salts. The solvent itself, owing to the action of Li+ ions, significantly interacted with mineral components of AC. It also occurred for basic oxides such as CaO and for metal oxides as MgO containing a small metal ion.

Correlation between the phase composition of composite YBa2Cu3O7−δ+xMeO superconductors and their strength characteristics

Experimental results on the doping of YBa2Cu3O7−δ superconducting ceramic with various metals (Ti, Zr, Ag, Hf, Ta, and W) are summarized. Some conclusions are drawn on the degree of chemical interaction between the metals and the main phase of the composite responsible for the superconducting properties of the material as a whole. An assessment is also made if the influence of doping on the strength characteristics, which vary in the composite as a result of different effects examined in this study.

Features of the interaction of boron with molten aluminum

1. In the reaction of solution of boron in molten aluminum during chemical interaction of boron fibers with molten aluminum, the properties of the fibers improve while in the reaction with the formation of aluminum borides they become poorer. 2. In liquid phase metallization of boron fibers at the aluminum coating-boron fiber interface the following phases are formed: a solid solution of boron in aluminum, AlB2 diboride, and the α-and β-modifications of AlB12 phase. Oxides and spinels were not detected at the fiber-coating interface. 3. Application of the matrix to the fiber by the continuous-casting method makes it possible to create a continuous interface of variable composition. Depending upon the degree of chemical interaction, the composition of the interface may be varied within wide limits without significant loss of strength of the fiber itself.

The kinetics of the uranium dioxide—Zircaloy reactions at high temperatures

Chemical interactions between uranium dioxide (UO 2) fuel and Zircaloy-4 (Zry) cladding material under Power Cooling Mismatch (PCM) conditions are described. The out-of-pile UO 2/Zry reaction experiments were performed with short Zircaloy tubular specimens filled with UO 2-pellets between 900 and 1500°C under variable UO 2/Zry contact pressures and under inert gas conditions. The annealing periods varied between 3 and 60 min. Due to the thermodynamic instability between UO 2 and Zry, UO 2 is partially reduced by Zry. The extent of UO 2/Zry reaction, as well as the composition of phases, depends decisively on whether or not good contact between UO 2 and Zry has been established. If solid contact exists, a (U, Zr)-alloy rich in uranium, as well as on oxygen stabilized α-Zr(O) phase are formed. The degree of chemical interaction between UO 2 and Zry is determined by oxygen diffusion in Zry and in the α-Zr(O)-phase formed. The UO 2/Zry reactions obey a parabolic time law; for the temperature dependence, the corresponding Arrhenius plot is given. Thin oxide layers on the cladding tube inner surface prevent UO 2/Zry reactions from taking place below 1100°C. Simulated fission products (cesium, iodine, tellurium) in UO 2 exert no influence on the extent of the reaction.

Network Formation and Reinforcement Studies with Terminally Brominated Polybutadiene

Abstract 1. It is possible to form essentially complete elastomeric network structures by the reaction of terminally functional polymers with multifunctional curative agents. The process occurs in two distinct rate steps: rapid reaction up to the region of the gel point, followed by much slower reaction of the remaining sites. 2. Reinforcement of such systems with carbon black, to provide strength properties similar to analogous conventional elastomers, is possible. Such reinforcement occurs in the absence of heat and of free-radical processes normally associated with the mastication and vulcanization of rubber. 3. Chemically inert particles (esterified silica) produce reinforcement effects similar to carbon black. When chemical interaction with the elastomer network is deliberately introduced, modulus increases and tensile strength declines. A slight degree of chemical interaction is not disadvantageous, but high levels of interaction result in severe loss of extensibility and strength.