Several thin layers of an arc plasma column were observed side-on at different distances from the cathode. The arc was operated in argon at atmospheric pressure with the arc current equal to 200 A. As the basic diagnostic method we used the Olsen - Richter diagrams. For determination of temperature the Larenz - Fowler - Milne and Boltzmann plot methods were applied. Electron density was measured from the Stark width of the ArII line and continuum intensity. The plasma near the cathode tip shows axial and radial dependence of its physical equilibrium state. In the hot core, the plasma is in LTE. Toward outer zones, the plasma state deviates from LTE. For plasma layers closer to the cathode, this deviation begins at smaller distances from the axis and for higher temperatures it vanishes for h > 3 mm. It is caused after all by the ArI ground state overpopulation. Theoretical estimations of the ArI ground state overpopulation give results consistent with experiment. Calculations show that this overpopulation is caused by inward transport of ground state atoms into the plasma column.

We studied the epoxy polymer surface modification using air plasma treatment in a Gliding Arc (GA) plasma reactor and a pulsed Dielectric Barrier Discharge (DBD). We employed optical emission spectroscopy (OES) measurements to approximate the vibrational and rotational temperatures for both plasma sources, as well as surface temperature measurements with fiber optics and IR thermography to corelate with the corresponding hydrophilization of the epoxy material. Water contact angle measurements revealed a rapid hydrophilization for both plasma sources, with a slightly more pronounced effect for the air DBD treatment. Ageing studies revealed stable hydrophilicity, with water contact angle saturating at values lower than 50°, corresponding to a >50% decrease compared to the untreated epoxy polymer. ATR-FTIR spectroscopy studies showed an additional absorption band assigned to carbonyl group, with its peak intensity being higher for the DBD treated surfaces. The spectra were also correlated with the surface functionalization via the relative peak area ratio of carbonyl to oxirane and benzene related bands. According to SEM imaging, GA plasma treatment led to no apparent morphological change, contrary to DBD treatment, which resulted in nano-roughness formation. The enhanced surface oxidation as well as the nano-roughness formation on epoxy surface with the air DBD treatment were found to be responsible for the stable hydrophilization.

Composition of the applied shielding gas has a strong influence on physical properties of the plasma and parameters of the welding process. In particular, increase of the percentage of carbon dioxide in argon results in an increase of the transition current value while changing from the globular to spray mode of metal transfer during the welding process. In order to explain this phenomenon, the MIG/MAG welding arc plasma was investigated for different mixtures of argon and carbon dioxide in the shielding gas. Applying a fast camera, recording distribution of spectral lines of the plasma components, we noticed some phenomena not described yet in the literature. Especially, there is a limit in the percentage of relative concentration CO2/Ar beyond which the arc shape is significantly modified.