Dielectricbarrier discharge treatment

Dielectric-barrier discharge treatment involves a metal high-voltage treatment electrode, a ground electrode, and an insulating material covering at least one electrode to allow for the formation of glow discharges at atmospheric pressure, as opposed to the formation of one or several localized streamers [8]. However, the dielectric-barrier discharge is not without streamers as it contains numerous micro-discharges that exist for nanoseconds [9]. These micro-discharges increase in number as treatment power or time is increased while the properties of individual micro-discharges remain constant [5]. Surface treatment occurs when 10-30 kV are applied across 1-3 mm gaps between treatment electrodes, ionizing the air in the gap that appears as a visible violet-blue corona [5, 10-14]. Figure 14.1 typifies the surface treater used in our research studies, which is representative of industrial dielectric-barrier discharge configurations designed for the surface treatment of moving webs.

Dielectric-barrier discharge treatment applies a low temperature plasma of approximately 27-35 °C [13, 14] to materials. In our laboratory, the application of dielectric-barrier discharge treatments to paper sheets formed from ligno-cellulosic fibers in a 1.5-mm treatment gap caused sheet temperatures to reach as much as 40 °C at high treatment levels when samples were passed repeatedly across treatment electrodes at 5 m/min as measured by Thermography [15]. A maximum temperature of 36-40 °C was confirmed using Cole Parmer temperature indicator strips [15]. Cold plasmas for surface treatment can also be generated using radio frequency waves and microwaves, which require vacuum conditions. In contrast, dielectric-barrier discharges can be performed at atmospheric conditions, making dielectric-barrier discharge technologies advantageous from a practical standpoint [16].

Stationary aluminum treatment electrode

15 kV AC generator

Plasma occurs in 1.0 -1.5 mm discharge gap

Stationary aluminum treatment electrode

Figure 14.1. Schematic for a dielectric-barrier discharge treater

At least one dielectric barrier material within treatment gap

Velocity controlled aluminum ground electrode

Figure 14.1. Schematic for a dielectric-barrier discharge treater

An atmospheric dielectric-barrier discharge plasma consists of photons [17], electrons [2, 5], free radicals [18], ions [2, 19], and excited molecules [20]. A major by-product of dielectric-barrier discharge is the production of ozone gas in the air [2]. When the high-energy electrons reach the surface of substrates, they have energies sufficient to break molecular bonds resulting in the creation of ions, free radicals, and other species on treated surfaces [10]. This leads to changes in surface energy, surface oxidation, cross-linking, broken bonds, disruption of surface layers, surface cleaning, and creation of free radicals on the surface of treated materials [10, 12, 21-23].

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