Mathematical modelling and optical emission spectroscopy are applied
to study the effect of the chamber pressure on the structure and properties of
supersonic plasma jets formed by a direct current arc. In this installation
the plasma is created inside the nozzle where the flow is accelerated. As a
result some deviation from thermal and ionization equilibrium can be found,
even at the working chamber inlet. In this paper, by means of a
two-temperature model, we study the argon jet flow using the data of the
emission spectroscopy measurements to make realistic assumptions about the
inlet boundary conditions. The results show that, when the chamber pressure is
low, a strongly underexpanded jet with a Mach disc is formed. For the higher
ambient pressure values, the core region of the jet changes to a mildly
underexpanded structure with alternating oblique expansion and compression
zones. The predicted shock zone positions are in a very good agreement with
measurement. The general analysis shows that the deviation from local
thermodynamic equilibrium in the jet is inversely related to the chamber
pressure. Along the jet core the deviation from thermal equilibrium is less in
the shock regions than in the expansion zones, where the electrons are heated
by three-particle recombination. Downstream of the jet core the velocity
drops, but the ionization and thermal equilibria are not attained because of
the correlation between the characteristic recombination and the hydrodynamic
times. Both the modelling and the emission spectroscopy show that the axial
electron number density is much closer to its frozen value than to
equilibrium value. The results obtained are helpful for different
applications such as plasma processing, rocket propulsion systems and the
simulation of re-entry conditions.
The aim of this work is to perform the polymerization compounding to improve the properties of Kevlar/PE composites. The approach consists in involving the surface of a reinforcement in a polymerization process of a polymer to be used either as a matrix in the final composite or as a special surface treatment to enhance solid/polymer interface properties in the composite. The polymerization compounding process is illustrated here with the polyaramid fibers as reinforcements and polyethylene as a matrix. The number of active sites on the fiber surface, initially insufficient to anchor the catalyst, were increased by a hydrolysis reaction prior to the polymerization. The anchored catalyst was subsequently used to conduct the Ziegler-Natta polymerization reaction of ethylene. The modified fibers were incorporated into the polyethylene resin to produce composites at fiber concentrations as high as 15 wt%. The morphology of the fibers and the composites was tested using electron microscopy. Finally, the mechanical properties of the composites (in impact and tensile tests) were measured to characterize the properties of model composites. POLYM. COMPOS., 27: 129 -137, 2006.
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