Marian C. Bazavan

Control of reactive species generation lies at the core of atmospheric-pressure plasma processing. In this work, we investigate the capability of a cold RF argon plasma jet source to produce reactive oxygen and nitrogen species (RONS) following the injection of a molecular gas (N₂ or O₂), either premixed with the main gas (Ar) or introduced separately into an already generated Ar discharge. We show that when reactive gases are injected directly into the Ar discharge, the range of operating parameters—particularly the ratio of reactive gas to main gas—is considerably widened compared to the conventional injection through the main argon flow. The plasma characteristics at the source exit were analyzed using Optical Emission Spectroscopy (OES), including the determination of electron density, rotational temperature, and the emission intensities of plasma species such as Ar I, NO(A), OH(A), and N₂(C), for both injection types. Overall, the results show that plasmas generated using in-discharge injection are more stable and capable of sustaining enhanced production of reactive radicals such as NO(A) and OH(A), whereas injection through the main gas can be tuned to selectively enhance NO generation. These findings highlight the potential of plasma sources employing premixed or in-discharge reactive gas injection for surface treatment and for the processing of gas and liquid phases.

A new method for the synthesis and deposition of tungsten oxide nanopowders directly on the surface of a carbon-fiber-reinforced polymer composite (CFRP) is presented. The CFRP was chosen because this material has very good thermal and mechanical properties and chemical resistance. Also, CFRPs have low melting points and are transparent under ionized radiation. The synthesis is based on the direct interaction between high-power-density microwaves and metallic wires to generate a high-temperature plasma in an oxygen-containing atmosphere, which afterward condenses as metallic oxide nanoparticles on the CFRP. During microwave discharge, the value of the electronic temperature of the plasma, estimated from Boltzmann plots, reached up to 4 eV, and tungsten oxide crystals with a size between 5 nm and 100 nm were obtained. Transmission electron microscopy (TEM) analysis of the tungsten oxide nanoparticles showed they were single crystals without any extended defects. Scanning electron microscopy (SEM) analysis showed that the surface of the CFRP sample does not degrade during microwave plasma deposition. The X-ray attenuation of CFRP samples covered with tungsten oxide nanopowder layers of 2 µm and 21 µm thickness was measured. The X-ray attenuation analysis indicated that the thin film with 2 µm thickness attenuated 10% of the photon flux with 20 to 29 KeV of energy, while the sample with 21 µm thickness attenuated 60% of the photon flux.