Band 26, Heft 1-2

No abstract available

The rheological properties and processing of polymer nanocomposites with dispersed nanometer-thick layered silicates are reviewed. The linear viscoelastic properties reflect the nanoscale dispersion of the silicate layers and the mesoscale structure that such dispersed layers or their aggregates form. The linear viscoelasticity exhibits time-temperature superpositioning, with the exception of systems in which dispersions are stabilized by hydrogen bonds. The non-linear stress relaxation behavior obeys time-strain separability, whereas large-amplitude oscillatory shear leads to strong alignment of the layers in the flow direction. The empirical Cox-Merz rule equating the steady shear viscosity and complex viscosity fails for these nanocomposites. It is conjectured that this results from orientation of the layers or their aggregates in response to a steady flow. Such orientation is also responsible for the silicate concentration independence of the first normal stress difference when compared at similar shear stress values.

This review paper discusses the dispersion of scalar released from a localized source in turbulent flows. In particular, the review emphasizes the distribution of scalar concentration in conjunction to environmental and industrial applications. Here, both general models of scalar concentration distributions, which appear in the literature and studies on specific aspects of the problem, are presented. Diverse subjects related to statistical descriptions of the scalar diffusion such as: location, size and distribution of the released scalar are discussed. These are characterized through models of probability density function of the scalar concentration and expected mass fraction. Experimental methods such as PIV and PLIF for measuring velocity and scalar concentration in turbulent flows as well as examples of applications are summarized.

Catalytic decomposition of methane into CO x -free hydrogen and carbon nanofibers has recently attracted much attention. The development of high-performance catalysts is essential for production of CO x -free hydrogen from methane. In this review we summarize the catalytic systems used for methane decomposition and compare catalysts with different active components and supports. According to the literature and our recent research results, Ni is the most active metal for methane decomposition and its catalytic performance can be enhanced by doping with metals such as Pd and Cu, especially for high reaction temperatures. The nature and origin of the surface are the main factors that influence the performance of carbon catalysts.

Commodity plastics such as polypropylene can be reinforced with lignocellulosic materials such as rice husk, available in the environment in abundance. Bonding between the polymer and rice husk can be improved by proper selection of compatibilizer or coupling agents. Thermoplastic composites thus prepared have potential applications in automotive industries and as good building material.