L. Aubrecht

PES fabric plasma modification

Polyester ranks the upper position in the world fiber production — nearly 54% of the total production of synthetic fibers. Troubles connected with minimizing of the textile hydrophobicity are usually being solved by the textile fibers’ surface chemical modification, but from ecological point of view modification of fabric with low temperature plasma is superior to classical chemical wet processes. Application of various plasmas for PES treatment has been already described. To compare the effectiveness of different plasma sources we performed a series of experiment both in RF and MW plasmas. For working gas nitrogen, oxygen and their mixtures were employed. Internal plasma control was provided by measurement of optical emission spectra. The hydrophilicity degree was determined by the drop test. Paper discusses optimal conditions of the PES fabric plasma treatment.

Application of atmospheric corona discharge for PES fabric modification

Polyester fabrics belong to often and regularly used materials in the textile industry. Traditional, mostly chemical methods of their processing often join with undesired environmental problems. The ecological requirements oblige to search and explore new and environmentally safer methods or technologies. One of them might be the cloth surface modification by means of atmospheric corona discharge. Paper presents connection between modification characteristics such as corona power input, duration of action, electrode optimisation and cloth sorption. It shows that the corona-modified cloth has an increased sorption and, probably, the touch.

Onset voltages of atmospheric corona discharges on coniferous trees

Abstract In this article, the phenomenon of generation of corona discharges on the tops of trees and plants is described. In the first part of the text, the conditions for generation of this electric field which leads to formation of corona discharge and transfer of electric charge between atmosphere and Earth, are discussed. Experimental results of the onset voltage and its dependence on the discharge parameters are presented. The coincidence between released species from corona burning point and surrounding atmosphere is also discussed. Equation for the calculation of critical intensity of the electric field and onset voltage in dependence on radius of the tip are also discussed and compared with experimental data and equations for current–voltage characteristics are described. The attempt to explain differences between theory and measured data is proposed.

Ion waves in a partially ionized gas in an external electric field

The propagation of longitudinal acoustic waves in the ion gas in an external electric field is studied theoretically. The results are compared with properties of waves in space without the external field. The phase velocities, damping factors and the influence of parameters of the gas on the properties of ion waves is discussed.

Onset voltages of atmospheric corona discharges on plants

In this article, experimental studies of the onset voltages and of the low current region of negative atmospheric corona discharge on trees are presented. Recent experiments show that the corona discharges on natural biological objects often differ from the classical discharges with metal electrodes. The onset voltage values lie in a wide range around the expected value. It has been found that the negative corona onset voltage of multiple point (such as the top of a coniferous tree) is higher than that of a single point. VA characteristics of multiple point coronas lie below those for a single point from the onset until a critical value is reached. From this point, the slope of the characteristics is steeper for the multipoint geometry. The effect of the multiple point configurations depends mainly on separation of needles. When the needles are closed together-the case of the needles of spruce or pine-the needles behave as a single needle. The difference may be caused by the presence of complex hydrocarbons released from the plants and the changes in the surrounding atmosphere.

Low frequency waves in a positive column of discharge

The propagation of longitudinal low frequency waves in the plasma of the positive column of a d.c. glow discharge is studied theoretically. The dispersion characteristics are obtained for conduction, ion acoustic and neutral acoustic waves. Equations are solved numerically and the results are compared with other theories and measurements.

GENERAL SOLUTION OF A SYSTEM OF EQUATIONS FOR ACOUSTIC WAVE PROPAGATION IN A PARTIALLY IONIZED GAS IN AN EXTERNAL ELECTRIC FIELD.

In this paper a system of equations describing the propagation of acoustic waves in multicomponent partially ionized plasma in an external electric field is solved generally, when these waves are generated by an external neutral sound wave in plasma. The equations are solved by means of Laplace transformation. It has been found that a sound wave generates a group of waves with different frequencies and wave vectors. For the sake of comparison, the solution without an external field and the linear solution in the form of waves having the same frequencies as the frequency of the excitation wave are given.

Nonlinear theory of acoustic wave interaction with laser discharge

The problem of gas laser modulation by acoustic wave is studied theoretically. Theoretical treatment is based on the semiclassical theory of laser and on the theory of acoustic wave propagation in the positive column of d.c. glow discharge. The solution of basic equations is found and the analysis of obtained results is carried out.

MODULATION OF DISCHARGE PARAMETERS CAUSED BY ACOUSTIC WAVE.

The propagation of acoustic waves in a partially ionized plasma in an external electric field is studied theoretically. It is assumed that an acoustic wave propagating through ionized gas causes only perturbations in ion gas. The problem is studied in the hydrodynamic approach and the basic equation is solved by means of Laplace transformation. It was found that waves can propagate in plasma also at other frequencies and wave numbers except the wave with the frequency and wave number of the neutral sound wave. Relations are derived for the density of the perturbation current and the intensity of modulated light irradiated from the plasma and the possible mechanism of the interaction of an acoustic wave with a discharge is taken into account. The necessity of further theoretical and experimental investigation is shown in conclusion.

Application of atmospheric air plasma for polyethylene powder modification

Summary form only given. Since polyethylene and other polymers are due to their apolar structure characterized with low wettability and adhesion, large effort has been concentrated on finding new low-cost and environment friendly methods for improvement of their surface characteristics. Majority of experiments has been focused on polymer foils and films modification, but in spite of frequent use of polymer powders in industry research dealing with modification of powders is less common, probably due to problems of polymer powder aggregation and difficulties with manipulation. This contribution presents results of experiments made for testing of dielectric barrier discharge (DBD) usability for polyethylene (PE) powder modification. Experiments were provided in DBD reactor. Glass plate separated rectangular brass electrodes, one of them grounded and the second one connected to a high-voltage transformer. The distance between the electrodes was 14 mm. The powder particles were gravity-fed in a continuous stream through the air plasma zone from a hopper at the top to a collecting bin at the bottom of the reactor. PE powder batch was repeatedly filled in the plasma reactor channel, number of transits through the plasma reactor was one of investigated parameters. The AC high voltage supply was used in experiments. The wettability of the PE powder was determined with a tensiometer from dynamic capillarity rising measurements according to the Washburn method. Experiments proved substantial rise of polyethylene powder capillarity with increasing number of powder batch transits through the reactor. Modified powder exhibited also very good adhesion to metal surfaces. Important aspect for practical application of plasma-modified powder is the time-stability of the modification effect. Aging tests showed only very slow powder capillarity decrease in time, therefore modification effect seems to be stable in time