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We present some results obtained from nitriding of AISI 304 stainless steel substrates. The process take place in an inductively coupled plasma discharge supplied by a ∼300 W source at 13.56 MHz in a 85% hydrogen and 15% nitrogen gas mixture. The samples, placed into a pyrex glass discharge chamber (3.5 cm diameter and 60 cm long) were biased by DC power from 0 to −300 V with respect to ground. The resulting hardness is a function of the increasing nitrogen concentration in the substrate and this, in turn, of the temperature which varied from 200 to 470 °C. After nitriding at −300 V, hardness values of 1790 HV under 10 g loads and of 632 HV for 300 g were measured. X-ray diffraction indicates that the expanded phase amplitude (γN) depends on the substrate temperature.

We present in this work some experimental results obtained from nitriding AISI 304 stainless steel at different temperatures by means of RF/DC generated 10 15 m −3 density plasmas in the 1–4 eV electron temperature range. The samples were biased up to −400 V. Substrate temperatures have proved to be an influential factor in the diffusion of the ions impinging onto the material under treatment. In turn, the γ N shift expansion observed by XRD during this temperature increase is a function of the amount of nitrogen introduced to the sample and is related to the bias, the nitrided layer depth and the plasma characteristics. Thus, we have identified the substrate temperature as a global control variable in order to analyse the evolution of the nitrogen enrichment process through its influence on the X-ray diffraction imaging of the γ N shift in the samples. The optimization of the temperature is explored along with its limits in terms of the Cr precipitation threshold.

Dielectric barrier discharge cells (DBDCs) have proved their efficiency in the generation of cold plasmas for hazardous organic compound degradation. Here, we describe the design and construction of a dual thermal packed-bed reactor and DBDC-based system to carry out the degradation of hazardous organic compounds in both liquid and gas phases. The main components of this system are: (i) the thermal treatment system, (ii) DBDC and (iii) resonant inverters of low (3.3 kHz) and high (100 kHz) calculated frequencies. The definition of the cell physical parameters considers: (a) a first-order degradation ratio of the compound and (b) the air breakdown at atmospheric pressure as a function of the transport carrier gas. The power consumed by the cells during the discharges was computed theoretically and experimentally. Using the dual system along with a gas chromatography diagnostic system, highly efficient degradations of a test compound (benzene) have been obtained, reaching 99.950% in the case of a cell experimentally operated at 3.3 kHz and up to 99.996% in another one at 94.3 kHz. An additional 3.7 times reduction in the latter case residence time with respect to the low frequency cell has been found.

Significant improvements in the surface properties of austenitic AISI 304 stainless steel by the use of PIII technology in nitrogen plasmas have been demonstrated. Yet, such treatments, often focused on the development of microhardness, can affect adversely the corrosion performance of the samples. Several results in this direction are presented in this work which have been obtained from the PIII processing of stainless steel plates in a nitrogen plasma within a toroidal chamber. This geometry presents a potential for turbulence which, in turn, should enhance the collisional effects and better the plasma densities. The main relevant structural, mechanical and corrosion wise properties of the samples were analyzed by XRD, SEM, Vickers microhardness, surface profilometry and electrochemical methods. The results indicate that at a low temperature range (below some 250 °C) both microhardness and corrosion resistance improve. At middle temperature ranges (in the order of 250–400 °C) chromium nitride tends to precipitate affecting the austenitic phase and therefore leading to a decline in the tolerance to corrosion albeit to a substantial increase in the sample microhardness. Finally, at higher temperatures, microhardness grows dramatically along with the implantation depth while a significant reduction in the corrosion performance is observed.

In this paper, the design and construction of a high-voltage high-frequency serial resonant bridge inverter endowed with a fast resonant frequency following capability, using the digital phase locked loop (DPLL) technique, is described. The main characteristics of this inverter are: high voltage (10 kV), high frequency (94.3 kHz), and low losses in the commutation devices. This inverter is used for the excitation of a dielectric barrier discharge cell (DBDC) for cold plasma generation. The system has been applied in hazardous organic compound degradation. In particular, benzene has been degraded to the order of 99.85%, according to measurements obtained by gas chromatography.

A study is reported of the influence of both temperature and nitrogen gas pressure on the microhardness and corrosion resistance of AISI 304 stainless steel, PIII treated in a DC plasma discharge in a toroidal chamber. The sample temperatures were stabilised at various gas pressures within the range 1×10 −3 to 2×10 −1 mbar by adjusting the pulse duration (50–75 μs) while maintaining constant the bias voltage (−5 kV) and pulse frequency 1 kHz. It was found that treatment below ∼520 °C substantially enhances the microhardness as well as the corrosion resistance of the samples. The experiments also showed that treating the samples at temperatures above ∼520 °C adversely modifies the properties associated with corrosion resistance.

PIII technology has been applied in vacuum chambers with toroidal and cylindrical geometries in order to study the nitriding of AISI 304 austenitic stainless steel plates. A high voltage generator provided a 5 kV polarization in 5 μs long pulses at 1 kHz in a nitrogen plasma created by a DC source. An elemental analysis of the samples was performed by means of SEM while XRD was used to determine the characteristic patterns of their nitrides. Results indicate a significant increment in the implanted nitrogen content of the substrata. The detected nitrides were identified as Fe3NiN and FeNiN, which are associated with the enhanced austenitic phase of the stainless steel. Thus, the Vickers microhardness of the samples doubles in the cylindrical chamber and reaches a 2.8 times increase in the toroidal one. It is also observed that this microhardness tends to grow with the gas pressure, and therefore with the sample temperature, as well as with the thickness of the nitrided stratum.

Plasma immersion ion implantation (PIII) has proved to be a good method to implant ions into materials in order to modify their surface properties. In this article, we describe the design and construction of a small and low cost PIII device. The instrumentation consists of: (i) a simple plasma immersion experimental setup for ion implantation based on direct current glow discharges, (ii) a 25 kV pulse generator, (iii) an electrical probe system endowed with a guard to carry out diagnostics of the plasma parameters, and (iv) an automatic spectroscopy system for determining the plasma temperature. A study of the sheath expansion has been considered in order to fulfill the requirements of electron temperature, plasma density, high voltage bias, pulse frequency, and pulse duration for an adequate PIII process.

Among the applications of dielectric barrier discharge cells (DBDCs), the generation of cold plasmas for the degradation of toxic organic compounds has received a great deal of attention in recent years. Normally, a DBDC can be energized by means of a high voltage power supply operating at line frequency. In this paper, the analysis, design and construction of a power resonant seriesinverter is presented; this inverter is aimed to operate at high-voltages/high-frequencies, and its suitability to excite a DBDC is investigated. The topological analysis of the inverter is carried out using the fundamental approximation technique, where the DBDC has been modelled as a capacitor whose terminals' voltage is provided by a pulse transformer. Both, the DBDC and the pulse transformer are represented in an RLC equivalent circuit. The resonant inverter is designed to operate in a region where the transfer function is load dependent. The series resonant inverter performance has been experimentally tested in a DBDC app...

The simulation of a water purification system within a coaxial cylinder reactor operated by 1 kHz frequency plasma discharges in pre‐arcing regimes is presented. In contrast with precedent works, this computational model considers three mechanisms of the system operation: (a) the relevant physical characteristics of water, (b) the ionisation and expansion processes in the spark channel including the near‐breakdown electric current generated by the rate of change of the effective capacitance and resistance in the discharge, and (c) the energy associated with this initial spark in the water. The outcome of the model seems to meet all main requirements to allow the design and construction of specific water purification technology devices.

We present an experimental technique for decomposing nitrogen oxides by means of chemical processes of oxidation and reduction assisted by electric discharges taking place in a reactor designed for this effect. The plasma reactor consists of two flat aluminium electrodes of circular geometry with gas input and output accesses capable of increasing slightly the turbulence of the gas flux so to homogenize the mixture to be treated. Both electrodes are covered with a dielectric material. During the experimental phase, an N2 + NO (200 ppm) with slight proportions of O2 (

Some recent results obtained from nitriding AISI 304 stainless steel samples, 1.2 cm in diameter and 0.5 cm thick are reported here in the case of an 85% hydrogen and 15% nitrogen mixture work gas. The process was carried out from 300 to 400 W for (13.56 MHz) inductively coupled plasma within a 60 cm long pyrex glass tube 3.5 cm in diameter where the samples were biased up to −300 V with respect to earth. The resulting hardness appears to be a function of the substrate temperature which varied from 200 °C at a 0 V bias to 550 °C at −300 V. The plasma density at 400 W reached 3×1010 cm−3 with a 4 eV electron temperature. Prior to nitriding, all the samples were polished with 0.05 μm diamond paste, leading to a 30 nm average roughness (Ra). After nitriding at −300 V, the Ra rose until ∼400 nm while hardness values of 1500 HV under 300 g loads were measured. X ray diffraction indicates that the extended phase amplitude (γN), Fe and Cr nitride depends on the substrate temperature.

A non‐thermal atmospheric‐like plasma source able to operate at room temperature represents, by its physical nature, a considerable potential for biological applications, given its highly accurate action and extremely controllable penetration on the surface of biological tissue. As we start up a research line into this technology, we report the electrical characterization of a room pressure plasma discharge by means of a coupling network model. The discharge is produced by a 13.56MHz commercial generator. As it is impossible to measure directly its state variables (voltage and current intensity) due to the considerable perturbation created by introducing a low impedance at the system output, then an indirect estimation of such variables is achieved from experimental diagnostics at the input, so to validate the proposed electrical model.

In practical terms, those plasmas produced by a DC voltage power supply do not attain densities above the 108 to 109 cm−3 band. Here we present a power supply, controlled in current and voltage, which has been successfully designed and constructed delivering plasma densities in the orders of 109 – 1010 cm−3. Its experimental performance test was conducted within one toroidal and one cylindrical chambers capable of 29 and 35 litres, respectively, using nitrogen gas. The DC plasma was characterized by a double electric probe. Several physical phenomena present in the PIII process have been keenly investigated including plasma sheath dynamics, interaction of plasma and surface, etc. In this paper we analyze the effect of the implantation voltage, plasma density and pulse time in the PIII average heating power and fluence density.

A compact Matlab model of plasma discharges in a DBD reactor consisting of two parallel electrode plates with a small gap and a thin dielectric sheet between them is reported. Its DBD plasma is modelled as a voltage controlled current‐source switched on when the voltage across the gap exceeds the breakdown voltage. A three cell voltage‐source inverter, configured in half‐bridge, has been used as a power supply. This configuration has an excellent performance when operating as an open‐loop. The distribution of total energy between a large number of low power converters proofs to be advantageous, allowing an efficient high power drive. Simulation results show that the current source and its output current tend to follow an exponential behaviour. A phenomenological characteristic of the voltage‐current behaviour of DBD is then described by power laws with different voltage exponent function values.

Conventional wisdom assigns the DC glow discharge regime to plasma currents below ∼500 mA values, beyond which the discharge falls into the anomalous glow and the turbulent arc regimes. However, we have found evidence that, during toroidal discharges, this barrier can be ostensibly extended up to 800 mA. Thus, a computer simulation has been applied to the evolution of the main electrical characteristics of such a glow discharge plasma in a toroidal vessel in order to design and construct a respective voltage/current controlled source. This should be able to generate a DC plasma in the glow regime with which currents in the range 10−3–100 A can be experimented and 109–1010 cm−3 plasma densities can be achieved to PIII optimization purposes. The plasma is modelled as a voltage‐controlled current source able to be turned on whenever the breakdown voltage is reached across the gap between the anode and the vessel wall. The simulation outcome fits well our experimental measurements showing that the plasma curr...