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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. [ABSTRACT FROM AUTHOR]

Abstract: A study, both theoretical and experimental, of the steady regime of a glow discharge is reported where a nitrogen plasma is produced by a DC power source operating at a constant current through a 200–500 mA range. Two different models of this plasma are developed. The first one was designed to reproduce the V–I characteristic curve where the transition from the background ionization regime to the saturation one takes place, and, from this, to the Townsend and breakdown regimes, respectively. The second model represents the plasma behaviour as that of a voltage operated current source which follows the power law depending on the gas pressure as i(υ)= Aυ n(p). The experimental results confirm, to a high degree of coincidence, the predictions made by these models. [Copyright &y& Elsevier]

Abstract: A study of the plasma ion implantation (PIII) of commercially pure titanium (CpTi) at a low voltage (<4kV) is presented. The processed samples were treated in divers mixtures of O and N in order to achieve biocompatible oxidized and nitrided layers as well as to enhance their superficial hardness. In this way, the low wearing resistance of CpTi can be avoided while creating a biocompatible rutile phase titanium oxide layer for a better bone integration. A form of synergy associated to the dependence of microhardness on the implanted layer disposition is identified. Thus, an upper rutile layer is immediately followed by another one, in which titanium, a nitride (TiN0.26) and rutile coexist. The latter leads to a superior microhardness performance. Most of all these surface treatments of titanium, when applying an 80%N–20%O mixture, yield higher corrosion resistance parameters with respect to the main metallic materials used in prosthetics, including the Co–Cr–Mo alloys, albeit excluding CpTi. [Copyright &y& Elsevier]

Abstract: Better protective and functional coatings on dental drills are increasingly demanded for their desired mechanical, tribological or chemical properties. We have studied the surface modification of steel dental drills, with an aim to increasing both their cutting life and corrosion resistance in dentistry using low-energy plasma-immersion nitrogen implantation over different temperature ranges. The temperature of the drills was controlled by varying the implantation voltage. Following implantation, tests showed that the microhardness of the nitrided drill surfaces was approximately one order higher than that of untreated drills and the corrosion tolerance was found to increase with growing temperature of the plasma-immersion process. [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]

Abstract: Monitoring basic plasma parameters such as temperature (T), density (n), floating potential (Vf) or Debye length (λd) provides vital knowledge during the ion implantation processing of materials immersed in plasmas (PIII or PSII) generated either by DC or (13.56MHz) RF sources. Thus, a fully automated electromechanical system has been designed and constructed on the basis of guard double electric probes in order to prevent both probe erosion and plasma contamination. The electronic components of the system comprise a ±150V triangular and ramp wave form generator capable of supplying ±50μA to ±100mA currents at 1–2000Hz frequencies and a DAQ PCI-6023E data acquisition board with a 12 bit resolution compatible with LabVIEW graphic language. A program has been specifically developed for the latter in order to control the probe position within the discharge vessel and to capture, filter, visualize, process and store the respective information. The system has been experimentally applied to DC and RF plasmas of helium, argon, nitrogen, oxygen, and multiple gas mixtures with great success, inside several PIII reactors. Results are presented free from RF interference from the process itself or other surrounding sources. [Copyright &y& Elsevier]

Abstract: The superficial oxidation of pure titanium, 9mm diameter, 5mm thick disc samples by implantation and diffusion from inductively coupled plasmas is reported. Such rf plasmas were generated in a 15l cylindrical Pyrex-like glass chamber containing pure circulating oxygen. A quarter wavelength solenoidal antenna capable of transmitting 500W at 13.54MHz was externally wound around the chamber and connected to an rf generator capable of up to 1200W through an automatic matching network. The oxidation process was carried out for 6h periods while varying the gas pressure between 1×102 and 5×10−1 Pa and the sample bias up to −3000V DC. It was found that the sample temperature was a function both of the plasma density and the bias voltage. Without bias, the plasma heated the sample up to ∼200°C, and with maximal bias voltage, the substrate was heated to 680°C. At the latter temperature, the presence of the rutile phase was particularly evident in X-ray diffraction patterns. According to EDX data, the average oxygen to titanium ratio rose, from ∼0.06 for an untreated reference sample, to a ∼1.7 value for samples treated up to 680°C. [Copyright &y& Elsevier]