Several process variants of plasma nitriding can be distinguished depending on the location of the voltage introduction. The aim of this study is to compare three different variants of plasma nitriding (DC plasma nitriding, active screen plasma nitriding, and active screening process with bias voltage application) extended by the study of the coverage of active screen on C45E unalloyed steel, using two different N₂-H₂ gas mixtures. The thickness of the compound layer was measured using a scanning electron microscope, the phase analysis was performed by an x-ray diffractometer, and the nitrogen contents were analyzed by glow discharge optical electron spectroscopy. The results showed that the layer thickness and the surface hardness were higher by using active screen-biased plasma nitriding with high N₂ content gas mixture. Besides, the lid of the active screen did not influence significantly the chemical composition of the compound layer.

Chitosan coatings of 353 ± 12 nm thickness were prepared on glass and zinc substrates by dip-coating method to study their barrier-behaviour. The coatings were chemically modified to increase their degree of acetylation (DA) from ca. 44 % up to ca. 98 % resulting a quasi-chitin coating. The effect of the acetylation reaction was studied by infrared spectroscopy, and the structural changes of the native and acetylated coatings were investigated by UV-Vis spectrophotometry and X-ray diffraction. The surface properties of the coated samples were characterized by wettability measurements - advancing water contact angle decreased from ca. 80° (native) to ca. 43° (fully acetylated) - and microscopic (SEM, AFM) studies. The barrier behaviour of the chitosan layer depending on the DA was evaluated by electrochemical impedance spectroscopy studies and with a special mesoporous silica - chitosan bilayer system by measuring the amount of dye (Rhodamine 6G) accumulated in the silica through the chitosan coating during an impregnation step. These methods showed significant decrease in the barrier-effect of the coatings with increasing DA (accumulation of approximately six times more dye and a reduction of charge transfer resistance by an order of magnitude), due to the structural and ionization changes in the coatings.

Hydrophobic coatings from chitosan–surfactant composites (ca. 400 nm thick by UV-Vis spectroscopy) for possible corrosion protection were developed on glass and zinc substrates. The surfactants (sodium dodecyl sulfate, SDS or sodium dodecylbenzenesulfonate, and SDBS) were added to the chitosan by two methods: mixing the surfactants with the aqueous chitosan solutions before film deposition or impregnating the deposited chitosan films with surfactants from their aqueous solutions. For the mixed coatings, it was found that the lower surface tension of solutions (40–45 mN/m) corresponded to more hydrophobic (80–90°) coatings in every case. The hydrophobicity of the impregnated coatings was especially significant (88° for SDS and 100° for SDBS). Atomic force microscopy studies revealed a slight increase in roughness (max 1.005) for the most hydrophobic coatings. The accumulation of surfactants in the layer was only significant (0.8–1.0 sulfur atomic %) in the impregnated samples according to X-ray photoelectron spectroscopy. Polarization and electron impedance spectroscopy tests confirmed better barrier properties for these samples (40–50% pseudo-porosity instead of 94%). The degree of swelling in a water vapor atmosphere was significantly lower in the case of the impregnated coatings (ca. 25%) than that of the native ones (ca. 75%), measured by spectroscopic ellipsometry. Accordingly, good barrier layer properties require advantageous bulk properties in addition to surface hydrophobicity.