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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. [ABSTRACT FROM AUTHOR]

Abstract: Low-wetting low-hydrophilicity polipropylene fiber has been treated by means of non-thermal dielectric barrier discharge plasma. The fiber has been characterized before and after the treatment by scanning electron microscopy (SEM), X-ray diffraction, atomic force microscopy (AFM) and industrial tests of submersion in water. The cold plasma was generated in a helium–air mixture at a 2kHz frequency and 12–18kV potential. The treatment periods ranged from 1min up to 3min. The results present an increase in the oxygen content which rose from 2.5% to 4.8%. SEM analysis reveals a surface change of the fiber with the formation of nodules, which is confirmed by AFM. Water submersion experiments show an enhancement of the hydrophilic capability of the samples. [Copyright &y& Elsevier]

Abstract: Several theoretical and experimental studies have been carried out in recent years aimed at enhancing the mechanical resistance and osseo-integration of titanium based dental implants. The often inadequate mechanical properties of commercially pure titanium (CpTi) can lead to the clinical failure of dental materials. A plasma immersion ion implantation (PIII) process has been applied to CpTi samples in an optimized nitrogen/oxygen gas mixture at middle and high temperatures, improving considerably the properties of these. Studies of microhardness, corrosion, AFM, XRD and Raman spectroscopy have been applied in order to evaluate the treated samples whereby highly biocompatible TiO2 (Rutile) and TiNx layers have been identified. A high corrosion tolerance was found for CpTi, indicating a typical passive behavior of titanium, which can be attributed to a highly stable film formed on the samples placed in Hank's solution. The hardness was improved nearly five times with respect to that of the control material. [Copyright &y& Elsevier]

Abstract: Optimal surface nitriding is closely related to plasma chemical composition. The effects of Plasma-Immersion Ion Implantation (PIII) nitriding with 15% N2+85% H2 type mixtures have been studied. A simplified PIII facility was assembled around an evacuated Pyrex cylindrical 500 mm long reactor with a 190 mm inner diameter, over which a 3.2 mm wide antenna was coaxially wound with a 240 mm inner diameter. The system was supplied by a 13.56 MHz RF generator whose electric component developed the plasma discharge. After the admission of the gas mixture to the reactor vessel the breakdown took place within 5–15 Pa work pressure and 450–500W RF power. The main plasma parameters were characterized including a 1.8 × 1018 to 3.1 × 1018 m−3 density by means of double Langmuir probes. An additional DC power supply was selected in order to bias AISI 304 stainless steel samples with a view to improving the steel hardness properties without compromising its corrosion resistance. The samples treated at different temperatures and for several periods, were evaluated by means of X-ray diffraction (XRD), which indicated the formation of nitrides, identified as Fe3NiN and FeNiN and can be associated with the enhanced austenitic phase of the stainless steel. Scanning electron microscopy (SEM) assessed the atomic percentages of nitrogen both on the sample surface and through their cross-section. Vickers microhardness (HV) tests exhibited up to a 6–7 times increase at a 500g load. Finally, Raman spectroscopy studies established four active modes at 215, 267, 385 and 490 cm−1 with temperatures between 400 and 500 °C. [Copyright &y& Elsevier]