The Corrosion Enhancement due to Plasma Post-Oxidation Subsequent to Plasma Nitriding of a Steel AISI 4140

The corrosion enhancement due to plasma post-oxidation subsequent to plasma nitriding of the samples of low alloy annealed steel AISI 4140 was evaluated. The plasma nitriding was carried out at ≈570°C for 1-3 h in an atmosphere of 75% H₂ and 25% N₂. After this process post-oxidation at ≈450°C in a gas mixture, air and dry air-like was conducted for an hour. The treated samples were characterized using the XRD, SEM, AFM, potentiodynamic polarization and Vickers microhardness tests. The outcome of combined processes showed the presence of ε and γ' nitrided phases in the inner compound layer and in the outer one mostly of magnetite phase and barely visible of hematite one without using H₂ in the post-oxidation process. Also in these processes, the corrosion potential proved to be lower in the treated specimens than the untreated ones, and the corrosion current decreased up to one order of magnitude when treated in environment air and air-like ambient

Nitriding of 4140 Annealed Low Alloy Steel in RF Plasma

The annealed low alloy 4140 steel samples have been nitrided for different treatment periods (1-6 h) in an RF inductive plasma discharge with very low bias voltage ( ≈ 400 V). The resulting nitrided layer has been observed by means of an optical microscope whereas the nitride phases have been characterised by X-ray analysis. The corrosion response, assessed by the potentiodynamic tests in the 3.5% NaCl solution, presents both higher noble potential values and lower corrosion rates when compared with the untreated sample. The Vickers microhardness tests values show an appreciable increment compared to that of the untreated sample. The process is characterized by a high overall efficiency because similar average Vickers tests values were obtained, no matter for how long the treatment was extended. Likewise, the scanning electron micrographs confirmed no appreciable size evolution of the compound layer microstructure at different times of treatment

Aluminium Morphological Modification by Nitrogen-Argon Mixture PIII

With incident fluences of ≈ $10^{12}$ atoms/$cm^2$ aluminium samples have been plasma immersion ion implanted with either pure nitrogen or argon/nitrogen mixtures at temperatures around 450°C. X-ray diffraction studies have validated the formation of the cubic phase of AlN, in samples treated with both the gas mixtures and pure nitrogen. Likewise, the presence of the hexagonal phase of AlN has been detected when either pure nitrogen or a 70%N/30%Ar mixture have been used. The signature peak of AlN has also been confirmed by the Raman spectroscopy. The maximal microhardness values were found in samples treated with the mixture. The maximal roughness was achieved with the equal part mixture in all cases, although increasing with the implantation pulse width up to a 300 nm peak at 150 μs. The latter critical value remains invariant under the pure nitrogen plasma treatment, provided that implantation periods in the order of 4.5 h are carried out

N–O mix optimisation in low energy dense DC glow surface Ti conditioning

Samples of pure titanium have been treated by means a plasma immersed ion implantation (PIII) process in a DC glow discharge in pure oxygen and in different nitrogen-oxygen mixtures. In contrast with conventional voltage supply based glow PIII, the present study has been conducted with a novel specifically designed high current supply which allows a high electron density to be kept constant, regardless of gas pressure variations, within the operational ranks. Thus, the acquired sample characteristics can be more clearly ascribed to the chemical composition of the mixture. One stratified TiO2 (rutile) and TiN0.26 layer was identified from XRD and Raman spectroscopy, both of these compounds reputedly being highly biocompatible. The superficial hardness of the samples was improved up to more than five times that of the untreated reference sample, namely, ∼1600 Vickers microhardness (10 g load) thanks to a 2–6 μm deep implanted layer. These optimal results have been obtained from an 80% nitrogen 20% oxygen mixture at 1×10-2 torr. Furthermore, with this gas proportion, the best roughness finishing of the sample set was accomplished, which can be relevant for biocompatible applications

DBD reactor instrumentation for NO

The design and construction of an instrumentation for NOX degradation in a dielectric-barrier discharge reactor (DBDR) is presented. This is endowed with a parallel plane electrode glass-glass (GG) circular geometry configuration. A solid-state multi-cellular power supply was produced in order to generate the plasma discharge. The power supply is based on a full-bridge voltage inverter commanded by three 4.33 kHz square-wave signals. Thus, the output converter signal is filtered by a resonant LC circuit, providing a 13 kHz sine wave to the DBDR. Initial results showing high removal efficiencies of about 97% have been obtained by means of this instrumentation

Sequential Processes to Produce N-TiO2 Films Through Rf Plasmas

Using as target a CpTi disk in an atmosphere of argon/oxygen and by rf plasma. First titanium dioxide (TiO2) films were obtained on silicon substrates, and subsequently, these films were doped with nitrogen (N-TiO2). In both processes, along four hours at 390°C of temperature. X-Ray diffraction and Raman spectroscopy confirmed the presence of the nanostructured anatase phase. X-ray photoelectron spectroscopy analyzes indicate that the nitrogen atoms were incorporated into the TiO2 film with ~33.9 at%. The films reach a thickness of 1.25 μm and 40 nm the average uniformity determined by using an atomic force microscope. Finally, UV-Vis diffuse reflectance spectroscopy outcome evaluated ones an energy band gap reduction from 3.17 eV to 2.95 eV corresponding to TiO2 films and N-TiO2 films respectively

Sequential Processes to Produce N-TiO

Using as target a CpTi disk in an atmosphere of argon/oxygen and by rf plasma. First titanium dioxide (TiO2) films were obtained on silicon substrates, and subsequently, these films were doped with nitrogen (N-TiO2). In both processes, along four hours at 390°C of temperature. X-Ray diffraction and Raman spectroscopy confirmed the presence of the nanostructured anatase phase. X-ray photoelectron spectroscopy analyzes indicate that the nitrogen atoms were incorporated into the TiO2 film with ~33.9 at%. The films reach a thickness of 1.25 μm and 40 nm the average uniformity determined by using an atomic force microscope. Finally, UV-Vis diffuse reflectance spectroscopy outcome evaluated ones an energy band gap reduction from 3.17 eV to 2.95 eV corresponding to TiO2 films and N-TiO2 films respectively

Phenol degradation in aqueous solution by a gas-liquid phase DBD reactor

A dielectric barrier discharge (DBD) has been successfully applied to studying, both theoretically and experimentally, phenol degradation in waste water aqueous solutions. A coaxial reactor was selected where the liquid waste constitutes a part of the internal electrode itself, the liquid solution flowing up inside the hollow internal electrode impelled by a submersible pump. Thus, the solution falls by gravity on the external surface of the internal electrode. The DBD gas flows in parallel to the surface of the liquid. The cold plasma was generated from Ar-O2 mixture and O2 pure with the inclusion of moisture from the same solution. Two power supplies were compared delivering potentials up to 23 kV at 1.5 kHz, and up to 12 kV at 15.6 kHz respectively. The initial concentration of phenol was around 5 × 10−3 mol/L and efficiencies up to 99% were obtained after 1 h of treatment. Finally, a simplified kinetics model was developed where the temporal evolution of the compounds generated in the phenol degradation process was analyzed. Hydroquinone, catechol and resorcinol were obtained as byproducts and H2O, CO2 and some light carboxylic acids as final products

Instrumentation for a plasma needle applied to E. coli bacteria elimination

Microplasmas are nowadays a powerful tool with multiple practical applications. The performance of a specific instrumentation for a plasma needle capable of producing non-thermal plasmas and a DBD reactor able to produce atmospheric pressure plasmas, both of them designed and already constructed, is reported. These devices operate at 13.56 MHz and are driven by a specifically built radio frequency (RF) resonant converter. The reactors, which operate at atmospheric pressure in a He-air gas mixture at a 1.5 SLPM flow, have been successfully applied to eliminate E. coli bacteria. In the needle case, bacterial samples were submitted typically to a 500 V peak voltage plasma discharge for 120 s. In the DBD treatment, the samples were processed with typical 750 V peak voltage plasma discharges for 80 s. The sample pH was used as a criterion to measure the effectiveness of the plasma treatment, in such a way that the return to the basal pH value after the treatment can be assumed as the validation of the complete bacterial elimination