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Chlorobenzene (CB) is a toxic compound and is broadly used as a raw material for phenol, solvents, and agrochemical products, among other substances. CB being a very lightly soluble compound in water (~0.450 mL/L) is highly volatile, and it can be found in both liquid and gas phases. In this paper, the treatment of CB was carried out in an aqueous solution assisted by nonthermal plasma (NTP) generated by a dielectric barrier discharge. NTP was utilized as a generator, producing active species for the treatment of CB in both liquid and gas phases, attaining high degradation efficiencies >95% and using a low electric power consumption <20 W. Energy efficiencies of CB removal in kg/kWh were estimated, and relatively high values ~0.5 kg/kWh were obtained with a low-energy consumption. Attained degradation efficiencies were determined using gas chromatography and mass spectrometry. Optical emission spectroscopy study was conducted to determine the gas temperature during experimentations. Thus, the estimated magnitude was lower than 110 °C in overall cases. Meanwhile, the resulting excitation temperature was near to 0.2 eV. This magnitude is in the range of typical temperatures for similar NTP devices. [ABSTRACT FROM AUTHOR]

(1) Background: This study aims to evaluate the efficacy and safety of non-thermal plasma (NTP) therapy in accelerating wound healing in patients who have undergone laparoscopic and open surgeries. (2) Methods: NTP was applied using a needle-type reactor with an irradiance of 0.5 W/cm2 on the surgical wounds of fifty patients after obtaining informed consent. Three NTP treatments, each lasting three minutes, were administered hourly. (3) Results: The pilot study showed that NTP-treated surgical wounds healed completely without any signs of infection, dehiscence, pain, or itching. Notably, patients reported minimal pain after the NTP treatment. Visual assessments conducted twenty-four hours after surgery revealed no redness or fluid discharge. Comparisons with traditionally sutured wounds indicated that NTP-treated wounds healed at a rate equivalent to seven days. (4) Conclusions: The application of NTP in laparoscopic and open wounds proved safe and effective, expediting the wound healing process and eliminating clinical risks post-surgery. Significantly, NTP facilitated a healing rate within twenty-four hours, equivalent to seven days for suture-treated wounds, significantly reducing the hospitalization time to a single day. These findings highlight the potential of NTP to be a transformative approach for promoting postoperative recovery. [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]

Non-thermal plasmas (NTPs), known as cold atmospheric plasmas (CAPs), hold great potential for diverse medical applications, including dentistry. However, traditional linear and rigid dielectric barrier discharge reactors used for NTP generation encounter limitations in accessing oral cavities and root canals. To address this issue, we have developed an innovative NTP reactor featuring an angled end for improved accessibility. The central copper electrode, with a 0.59 mm diameter and adjustable length for desired angulation, is coated with zircon powder (ZrSiO4) to ensure stable NTP generation. This central electrode is housed within a stainless steel tube (3 mm internal diameter, 8 mm external diameter, and 100 mm length) with a 27° angle at one end, making it ergonomically suitable for oral applications. NTP generation involves polarizing the reactor electrodes with 13.56 MHz radio frequency signals, using helium gas as a working medium. We introduce plasma-treated water (PTW) as an adjunctive therapy to enhance biofilm eradication within root canals. A synergistic approach combining NTP and PTW is employed and compared to the gold standard (sodium hypochlorite, NaOCl), effectively neutralizing Enterococcus faecalis bacteria, even in scenarios involving biofilms. Moreover, applying NTP in both gaseous and liquid environments successfully achieves bacterial inactivation at varying treatment durations, demonstrating the device's suitability for medical use in treating root canal biofilms. The proposed NTP reactor, characterized by its innovative design, offers a practical and specific approach to plasma treatment in dental applications. It holds promise in combatting bacterial infections in root canals and oral cavities. [ABSTRACT FROM AUTHOR]

In this article, a novel class-E amplifier topology, based on the functioning principle of the stacked converters, is presented. In this amplifier the available output electric power is determined by the addition of the electric power generated by each of the associated devices. Herein, two MOSFETs connected in series are linked, on the one hand, to a dc voltage source and, on the other hand, to a resonant LC circuit and a resistance charge connected in parallel to the capacitor. Both MOSFETs are driven by a gate-to-source square signal allowing a synchronized commutation, promoting a quasi-resonant amplifier behavior similar to that of the classical class-E amplifier; with the characteristic of being able to manage the double of applied dc voltage amplitude and to supply twice electric power to the same load in comparison with the class-E amplifier. This device is able to distribute the same electric power between both MOSFETs, reducing at almost half the magnitude of applied drain-to-source voltage. As a result, voltage stress of each power switch is reduced in comparison with the typical class-E amplifier. Drain efficiency (DE), power added efficiency, and gain of the proposed device were obtained in function of the applied dc voltage. [ABSTRACT FROM AUTHOR]

Objective: an innovative non−thermal plasma (NTP) system constituted by a radiofrequency (RF) power generator directly coupled to a treatment probe is described and characterized. This system is intended to be applied as a medical device for therapeutic treatments. Methods: electrical characterization of the radiofrequency power generator supplying the treatment probe was performed. Meanwhile, generated NTP was optically analyzed. Obtained data were studied to establish the safety profile of plasma application on heat sensitive matter. Results: the NTP system was validated through bacterial deactivation trials, as well as, of being capable of deactivating carcinogenic cells. Besides promoting and accelerating wound closure in vivo performed in mice, demonstrating faster healing than that done with conventional treatments. Conclusion: the NTP system's characterization is an essential stage to determine the adequate application of the generated plasma over organic media. The therapeutic benefits of the NTP system were proved by the development of in vivo experiences involving laboratory mice. Significance: the generated NTP interacts with surrounding air particles producing reactive oxygen and nitrogen species, which, exhibit bactericidal and antiseptic effects due to their strong biochemical reactivity; functioning like critical mediators in animal physiology and promoting wound healing processes. These properties make the NTP system a feasible technology intended for therapeutic treatments. [ABSTRACT FROM AUTHOR]

In this paper, we present the inactivation study of bacteria suspended in water by atmospheric pressure nonthermal plasma generated by pulsed dielectric barrier discharges (PDBD) in a wire-cylinder reactor. The experiments were carried out with Gram-positive Bacillus subtilis bacteria at an initial concentration of $1 \times 10^{6}\,\,\text {cells}\cdot \text {mL}^{-1}$. Bacterial inactivation was analyzed comparing two different types of treatments: bacteria in contact with distilled water previously exposed to plasma (indirect plasma treatment) and bacterial suspension in direct contact with plasma (direct plasma treatment). Plate count, microscopy, and spectrophotometry methods were used to study the bactericidal action of the PDBD. The obtained results indicated that both treatments eliminate bacteria, where direct plasma treatment led to a faster biodecontamination with a 4.87 – log10 reduction in 10 min than 2.36 – log10 reduction achieved with indirect plasma treatment. Microscopic observations reveal that treated bacteria were damaged suggesting the disruption of their cell walls during the direct plasma treatment. [ABSTRACT FROM AUTHOR]

In this paper, the research about the formation and growth of nano- and micro- particles of silver from a silver-modified natural zeolite (Ag-zeolite) by pulsed dielectric barrier discharges (PDBD) is presented. The antibacterial activity of the silver obtained was also considered. Ag-zeolite was exposed to plasma generated by PDBD in distilled water, obtaining a broad range of Ag particles at pressure and room temperature, without using additives, chemical reducing agents or stabilizers. The relationship between the Ag particle size and the contact time with the plasma shows that: (a) at short exposure periods with the plasma are enough to get nanoparticles, and (b) at longer time exposure, microparticles were formed with a regular space distribution over the Ag-zeolite. The particle size was estimated by scanning electron microscopy and the silver identified through X-ray diffractometry, energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy. The antibacterial activity of the modified Ag-zeolite was determined qualitatively against Escherichia coli based on the zone of inhibition produced. [ABSTRACT FROM AUTHOR]

The survival of Escherichia coli bacteria and mouse glioma cells were studied under different temperatures using direct heating in water, ultrasound, and magnetic fluid hyperthermia. The survival of these microorganisms depended on whether the heating mode was continuous or discontinuous, surviving more in the former than in the discontinuous heating mode. Whereas Escherichia coli bacteria did not survive at temperatures ≥50C, the mouse glioma cells did not survive at temperatures ≥48C. The survival of both these microorganisms was independent of the presence or absence of the magnetic nanoparticles of magnetite, suggesting that these, having mean particle sizes of 9.5, 8.5 and 5, did not show any apparent cytotoxicity effect. Present results also showed that the inductive heating system which used a radiofrequency of 13.56 MHz, providing a maximum magnetic field strength of 160 A/m, the electric rather than magnetic heating predominated. [ABSTRACT FROM AUTHOR]

In this paper, we present the evaluation of a DBD reactor that generates an energy per pulse of 65.3 mJ in order to inactivate E. coli ATCC 8739 at 10^3 , 10^6 , and 10^8 CFU/mL order concentrations and E. cloacae CDBB-B-963 at 10^3 and 10^7 CFU/mL order concentrations, in a volume of water flowing continuously. Particularly, experimentation is focused in 500 mL, under atmospheric pressure. The DBD reactor was coupled to a peristaltic pump type, a cooling jacket, containers for water in treatment and cooling fluid, and systems to monitor the experimental conditions. The implementation of the experiments was carried out at three different fluid flow rates: 2.0±0.1, 3.5±0.1, and 4.4±0.1 mL/s; in each of them the time required to carry out a cycle of treatment corresponded to 256±7, 143±2, and 113±1 s, respectively. During the DBD application, water flowed continuously at recirculation mode, promoting the continuous oxygen injection at 8.3 mL/s. In the three established fluid flow rates, the efficacy of treatment reached 100% in inactivation of E. coli bacteria at 10^3 and 10^6 order concentrations at the end of the first cycle of treatment. At 10^8 CFU/mL order concentration, complete inactivation of E. coli bacteria was achieved at the end of the fourth cycle of treatment. Meanwhile, E. cloacae bacteria showed an inactivation of 100% at the end of the first cycle of treatment at 10^3 order concentration; when the order concentration increased to 10^7 , the efficacy of the process depended on the fluid flow rate, at 3.5 ± 0.1 and 2.0 ± 0.1 mL/s survival was 0% at the end of the first cycle of treatment; nevertheless, at the highest (4.4 ± 0.1 mL/s), an additional cycle was required. [ABSTRACT FROM AUTHOR]

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]

The design and construction of a full-bridge flying capacitor multicell inverter (FCMI) composed of two legs is disclosed. Each leg consists of three switching cells. In order to control the power converter, a square wave signal switching technique has been used; the converter output frequency has increased at three times the switching frequency. Moreover, the system can be tuned by a variable inductor coupled with a high-voltage transformer allowing the FCMI to work under a resonance condition from 10- to 30-kHz frequency range. The goal of this converter is to generate a dielectric barrier discharge (DBD) at atmospheric pressure applied in environmental remediation and biological interaction studies. The proposed inverter has been tested with two different DBD reactors, one of them intended for the degradation of organic compound metacresol dissolved in water. [ABSTRACT FROM PUBLISHER]

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]

Background and Aims: The efficacy of a direct application of plasma needle to in vivo wound healing was experimentally studied in mice. This kind of plasma has achieved considerable success in blood coagulation and tissue restoration in mice. In the development of the present study, an argon plasma needle was chosen for coagulation purposes, whereas for healing purposes, a helium plasma needle was used. Methods: Treatment was applied with a plasma needle produced by argon and helium to a wound induced in laboratory mice. Tissue regeneration was carried out by three argon plasma treatments with 0.5 SLPM flow for 1 min and three treatments of helium with 1.5 SLPM flow. Intervals between each treatment were 5 min and 60 min for argon and helium plasmas, respectively, thus completing a total treatment time of 180 min. Histological sections were performed to corroborate the internal bleeding and tissue regeneration. Results: After three treatments with argon plasma, the blood produced in the wound was coagulated and protein material appeared. By means of treatment with helium plasma, an approach of the wound edges was produced until the conclusion thereof. These results were corroborated histologically. Conclusions: This type of acceleration during the skin wound healing process can be attributed to the formation of reactive species such as NO, which were increased in the helium plasma needle with respect to the argon plasma needle. [ABSTRACT FROM AUTHOR]

This paper presents an experimental study of the inactivation in water of two representative classes of bacteria, Gram-negative Escherichia coli and Gram-positive Bacillus subtilis, using pulsed dielectric barrier discharges (PDBDs) in a coaxial arrangement. To this purpose, an adjustable plasma source supplies 25-kV/500-Hz pulses, 30 \mu\s long, at atmospheric pressure, with total energy consumption estimated at about 100 mJ/pulse. The inactivation effect of a PDBD on these types of microorganisms has been previously studied in dependence on an oxygen gas flow mode (null, continuous, and modulate). The results have shown a significant bacterial reduction rate from 10^8 to 10^3\ \cells/mL with E. coli and from 10^7 to 10^3\ \cells/mL with B. subtilis. The inactivation effectiveness is substantially similar in both kinds of bacteria, although some data suggest a greater susceptibility of the Gram-negative E. coli to plasma exposure. Plasma diagnostics was carried out using optical emission spectroscopy whereby the OH radical and reactive oxygen species formation rates in solution were found and the level of ozone produced by the discharge was monitored. Finally, a kinetics model was developed to characterize the chemical species taking place in nonthermal plasma inactivation processes in water. [ABSTRACT FROM PUBLISHER]

An experimental study of ATCC (American Type Culture Collection) 8739 Escherichia coli bacteria inactivation in water by means of pulsed dielectric barrier discharge (PDBD) atmospheric pressure plasmas is presented. Plasma is generated by an adjustable power source capable of supplying high voltage 25 kV puises, -30 Fs long and at a 500 Hz frequency. The process was conducted in a ~152 cm³ cylindrical stainless steel coaxial reactor, endowed with a straight central electrode and a gas inlet. The bacterial concentration in water was varied from 103 up to 108 E. coli cells per millilitre. The inactivation was achieved without gas flow in the order of 82% at 108 colony-forming units per millilitre (CFU mL-1) concentrations in 600 s. In addition, oxygen was added to the gas supply in order to increase the ozone content in the process, raising the inactivation percentage to the order of 90% in the same treatment time. In order to reach a higher efficiency however, oxygen injection modulation is applied, leading to inactivation percentages above 99.99%. These results are similarly valid for lower bacterial concentrations. [ABSTRACT FROM AUTHOR]

With incident fluences of ≈ 1012 atoms/cm² 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. [ABSTRACT FROM AUTHOR]

The design and construction of a 13.56-MHz RF power amplifier has been carried out on the basis of a modified resonant LC circuit in parallel regarding to the classic E-class amplifier LC series resonant circuit; this was done in order to take advantage of the operation characteristics of the resonant capacitor as a bidirectional voltage source. Therefore, the parallel LC circuit amplifies the voltage signals which can be applied to resistive or capacitive–resistive loads without the need for an impedance matching network, conventionally used with plasma generators. The main achievement of the described instrumentation lays in its constant response under a wide interval of load impedance. This facility has been applied to the generation of steady discharges in plasma needle appliances and both parallel plate and coaxial dielectric barrier discharge (DBD) reactors. Some relevant results of the DBD sterilization of four different kinds of microorganisms are included, showing the feasibility of the technique within reduced processing times, under 80 s in all the cases. [ABSTRACT FROM PUBLISHER]

Abstract: Films of titanium dioxide (TiO2) in the rutile and anatase phases have been obtained in a cylindrical pyrex-like glass vessel inductively coupled to a 13.56MHz radio frequency generator. Rutile films were developed from commercially pure (CpTi) titanium samples used as targets in an argon/oxygen plasma. Each CpTi target was biased at −3000V by means of a direct current supply. The plasma ion acceleration at such a potential leads to a kinetic energy transference to the target whose temperature rises to ∼670°C, favourable to the rutile formation. The anatase films were obtained from sputtering the titanium targets over glass and silicon electrically floated substrates. The latter were placed 3cm away from the target. The substrates attained a temperature resulting from the amount of heat transferred by the plasma particles, in turn, a function of the plasma parameters. Thus, under the prevailing experimental conditions, substrate temperatures lay in the ∼280 to 325°C range. Atomic titanium is assumed to be sputtered out of the target and oxidised, evolving into the anatase phase on the surface of the glass or silicon. The obtained film phases did not require annealing after the plasma oxidation process. The characterisation of the film samples was conducted by means of X-ray diffraction (XRD), Raman spectroscopy and scanning electron microscopy (SEM). [Copyright &y& Elsevier]

Abstract: It is not easy, in general, to improve the mechanical properties of aluminium alloys by traditional nitriding methods. By contrast, plasma immersion ion implantation (PIII) has been successfully used for hardening and in wear resistance improvement. The present work sets out to investigate the formation of AlN on 6061T6 aluminium samples by the PIII process at low energy (2–6keV) with ion doses in the order of 1018 ions/cm2 and from nitrogen–argon mixtures at different concentrations (N70–Ar30, N50–Ar50 and N30–Ar70) maintained at ∼400°C sample temperatures. The outcome was evaluated by X-ray diffractometry, scanning electron microscopy, Vickers microhardness tests and profilometry. [Copyright &y& Elsevier]

The design, instrumentation and early operation results of a digitally controlled voltage source inverter (VSI) are described. This inverter has been structured from a three cell flying capacitor inverter (TCFCI). Two different inverter control modes - open-loop and closed-loop - are applied by a digital system based on a Texas Instrument TMS320C6713 digital signal processor (DSP) board. The VSI is able to generate AC voltage signals up to 120 V amplitudes at a maximal 6 A current, from ∼9 kHz to ∼60 kHz in ∼900 Hz steps in both controls by varying the signal period through the square-wave command strategy. The multi-cell structure of the inverter provides an output frequency nearly three times that of the TCFCI semiconductor commutation. The power output of the TCFCI can drive a high frequency step-up transformer which, in turn, is associated with a cylindrical reactor where dielectric barrier discharges (DBD) are conducted. [ABSTRACT FROM AUTHOR]

Abstract: It is not easy, in general, to improve the mechanical properties of aluminium alloys by traditional nitriding methods. By contrast, plasma immersion ion implantation (PIII) has been successfully used for hardening and in wear resistance improvement. The present work sets out to investigate the formation of AlN on 6061T6 aluminium samples by the PIII process at low energy (2–6keV) with ion doses in the order of 1018 ions/cm2 and from nitrogen–argon mixtures at different concentrations (N70–Ar30, N50–Ar50 and N30–Ar70) maintained at ∼400°C sample temperatures. The outcome was evaluated by X-ray diffractometry, scanning electron microscopy, Vickers microhardness tests and profilometry. [Copyright &y& Elsevier]

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 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]

This paper presents a model of the typical dielectric barrier plasma discharge at atmospheric pressure, structured as an equivalent electric circuit whose elements are identified with, and deducted from, the main influential variables of the process, namely, the applied gas, the geometry of the reactor, the breakdown parameters, as well as the power supply associated to the dielectric barrier discharge cell. Considering a parallel-plate reactor and a high-voltage sinusoidal power supply, an electrical comprehensive Simulink/MATLAB model has been developed in order to reveal the interaction between these two elements. The main components of this discharge model are as follows: 1) a double dielectric capacitance; 2) a voltage-controlled current source; and 3) a gas capacitance associated to the ionized gas. A sinusoidal voltage of up to 15 kV peak to peak at frequencies of 12.5 and 47 kHz has been applied to the discharge electrodes. The electrical model is based on the power law proposed by Roth, which defines the V --I behavior during the discharge startup. A series of simulations has been carried out in order to estimate the total current and voltage consumed during each discharge and to identify those parameters which are not measurable during the process. Finally, both the experimental and simulated voltage and current results in helium, argon, and nitrogen, as well as their Q--V graphics, are shown, and a comparison between them is discussed. [ABSTRACT FROM AUTHOR]

• The development of a DBD reactor to evaluate the bacterial inactivation in water. • Efficiency of treatment with a 6 log10 reduction for E. coli and S. typhi. • 12 kV with oxygen was the minimum voltage to inactivate E. coli and S. typhi. This work presents the study of the voltage and oxygen effect on bacterial inactivation in water using a pulsed dielectric barrier discharge (DBD) under atmospheric pressure, where Escherichia coli (E. coli) and Salmonella typhi (S. typhi) bacteria were used as model microorganisms. A cylindrical DBD reactor was developed and tested in applications to assay the efficiency of bacterial inactivation in water on a volume of 500 mL flowing continuously throughout the system assisted with a peristaltic pump at 4.4 ± 0.1 mL/s. The efficiency of the treatment reached a 6-log 10 reduction for both E. coli and S. typhi bacteria at 106 CFU/mL of concentration at the end of the first cycle of treatment at a minimum voltage of 12 kV with oxygen bubbling gas, concluding that there was a minimum voltage to produce inactivation of E. coli and S. typhi samples. Bacterial inactivation without the oxygen condition contrasted with the high rate of inactivation with oxygen at relatively low voltage discharges. [ABSTRACT FROM AUTHOR]

Abstract: 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 ∼300W source at 13.56MHz in a 85% hydrogen and 15% nitrogen gas mixture. The samples, placed into a pyrex glass discharge chamber (3.5cm diameter and 60cm long) were biased by DC power from 0 to −300V 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 −300V, hardness values of 1790 HV under 10g loads and of 632 HV for 300g were measured. X-ray diffraction indicates that the expanded phase amplitude (γ N) depends on the substrate temperature. [Copyright &y& Elsevier]

In this paper, we present a model (which is structured as an equivalent electric circuit whose elements are identified and deducted from the nature of the medium, the ionization and expansion process of the streamers that convey the prebreakdown current, and the energy associated to the electric breakdown in water) and a simulation of a pulsed corona discharge (PCD). Considering this, a coaxial reactor and an inexpensive and compact high-voltage pulsed-power. supply (PPS) system were designed and constructed with the purpose of carrying out the PCD experimentally. The simulation results enable the prediction of the behavior of the discharge. The coaxial reactor is constituted by a cylindrical chamber and a straight central rod. The PPS operates within the 100-2000-Hz repetition rate and 0-30-kV amplitude ranges. All the system has been tested, and the first electrical results, voltage, and current waveforms, are presented. [ABSTRACT FROM AUTHOR]

Abstract: We present in this work some experimental results obtained from nitriding AISI 304 stainless steel at different temperatures by means of RF/DC generated 1015 m−3 density plasmas in the 1–4eV electron temperature range. The samples were biased up to −400V. 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. [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: Microplasmas represent, by their physical nature, a considerable potential for medical applications given their highly accurate action and extremely controllable penetration on the surface of biological tissue. This plasma modality is today a powerful tool in practical applications such as the elimination of necrotic cells or the sterilization of dental cavities. As we start up a research line into this technology, we have constructed a plasma needle capable of producing non thermal plasmas, within a 1 mm radius, produced by a typical 13.56 MHz RF generator. The plasma is developed out of helium and argon. Initial electrical tests show that the plasma needle can operate at comparatively low voltages (peak to peak 100–250 V) and low power consumption. With a view to optimizing the medical applicability of the system, a study of the effects of plasma temperature and power variation at different distances is presented. [Copyright &y& Elsevier]

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: 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. [Copyright &y& Elsevier]

Abstract: 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 (50–75μs) while maintaining constant the bias voltage (−5kV) and pulse frequency 1kHz. 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. [Copyright &y& Elsevier]

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 e  ciency 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. [ABSTRACT FROM AUTHOR]

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: We present a study on the surface modification of dental tools by nitrogen PIII with a view to increasing both their cutting life and corrosion resistance. The treatment temperature was selected between 350 and 500°C, every 50°C, being controlled by varying the pulse duration in order to determine the improvement of the material performance after implantation. The tools were additionally characterized by Knoop microhardness measurements, SEM, XDR and electrochemical corrosion tests which, in all, pointed to an abundance of the supersaturated iron phase accompanied by considerable increases in microhardness and yet, with a slightly enhanced corrosion resistance. Furthermore, the formation of the associated expanded austenitic phase appears to enhance the corrosion resistance of the untreated drills. [Copyright &y& Elsevier]

We propose a novel combined system of pulsed dielectric barrier discharges (PDBDs) and silver-modified natural zeolite (Ag–zeolite) in liquid in bubbles. The system was tested with the Escherichia coli bacteria immersed in water. In order to evaluate the efficiency of the system in bacterial inactivation a microbiological analysis was carried out; 9.82-ln of bacterial reduction was obtained using the combined system, whereas 0.43-ln of bacterial reduction was obtained using Ag–zeolite alone, and 6.26-ln with PDBD. The elapsed time was 10 minutes for the three treatments. [ABSTRACT FROM AUTHOR]

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]