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In developing countries, death due to diseases caused by fecal-oral ingestion can be avoided by taking action on drinking water issues. Adequate access to water treatment systems to reduce infections is a critical cause. Silver has been used as an antibacterial product, including biomedical applications. Therefore, in this paper, the effect of the chemical speciation of silver from silver-modified zeolite-rich tuffs on the mortality of Escherichia coli (E. coli), Streptococcus faecalis (S. faecalis) and Candida albicans (C. albicans) suspended in aqueous solution was investigated for disinfection purposes. The following aspects were considered to develop the investigation: a) the technique to prepare the modified zeolitic materials, either with ionic silver or silver nanoparticles, which were obtained in two ways: one, with grapefruit extract and the second, by using non-thermal plasma generated in a dielectric barrier discharge reactor of parallel plates; b) the response of the prokaryotes (bacteria) and eukaryote (yeast) microorganisms to disinfectant agents in batch systems; c) the disinfection processes as a function of time to obtain kinetics parameters; and d) the kinetics of the silver release from the silver-modified zeolite-rich tuffs, considering the models of Higuchi and Korsmeyer. The zeolitic materials were characterized by low-vacuum scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), transmission electron microscopy (TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The non-thermal plasma reduced ionic silver is more efficient at generating silver compounds with several oxidation states, which are essential during the microbial inhibition process. For the bacterial (E. coli and S. faecalis), the materials with nanoparticles were efficient to inactivate them. However, the yeast (C. albicans) reaches the total inactivation when the zeolitic material contains ionic silver in the crystalline network. The E. coli, S. faecalis and C. albicans survival behavior suspended in aqueous solutions after contact with Ag-modified natural zeolites depends on the chemical speciation of the silver present in these materials, Ag+1 in the case of OAgiZ or nanoparticles of Ago promoted by the grapefruit extract (OAgnpTZ), as well as by non-thermal plasma generated in a dielectric barrier discharge reactor of parallel plates (OAgnpPZ). In general, the concentration of silver in the aqueous solution after the disinfection process cannot exceed the recommended levels established for international organizations. The OAgnpPZ is a potential microbicide agent against E. coli and C. albicans, and the OAgnpTZ for F. faecalis.

BACKGROUND: In developing countries, death due to diseases caused by fecal-oral ingestion can be avoided by taking action on drinking water issues. Adequate access to water treatment systems to reduce infections is a critical cause. Silver has been used as an antibacterial product, including biomedical applications. Therefore, in this paper, the effect of the chemical speciation of silver from silver-modified zeolite-rich tuffs on the mortality of Escherichia coli (E. coli), Streptococcus faecalis (S. faecalis) and Candida albicans (C. albicans) suspended in aqueous solution was investigated for disinfection purposes. METHODS: The following aspects were considered to develop the investigation: a) the technique to prepare the modified zeolitic materials, either with ionic silver or silver nanoparticles, which were obtained in two ways: one, with grapefruit extract and the second, by using non-thermal plasma generated in a dielectric barrier discharge reactor of parallel plates; b) the response of the prokaryotes (bacteria) and eukaryote (yeast) microorganisms to disinfectant agents in batch systems; c) the disinfection processes as a function of time to obtain kinetics parameters; and d) the kinetics of the silver release from the silver-modified zeolite-rich tuffs, considering the models of Higuchi and Korsmeyer. The zeolitic materials were characterized by low-vacuum scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), transmission electron microscopy (TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). RESULTS: The non-thermal plasma reduced ionic silver is more efficient at generating silver compounds with several oxidation states, which are essential during the microbial inhibition process. For the bacterial (E. coli and S. faecalis), the materials with nanoparticles were efficient to inactivate them. However, the yeast (C. albicans) reaches the total inactivation when the zeolitic material contains ionic silver in the crystalline network. CONCLUSION: The E. coli, S. faecalis and C. albicans survival behavior suspended in aqueous solutions after contact with Ag-modified natural zeolites depends on the chemical speciation of the silver present in these materials, Ag(+1) in the case of OAg(i)Z or nanoparticles of Ag(o) promoted by the grapefruit extract (OAg(npT)Z), as well as by non-thermal plasma generated in a dielectric barrier discharge reactor of parallel plates (OAg(npP)Z). In general, the concentration of silver in the aqueous solution after the disinfection process cannot exceed the recommended levels established for international organizations. The OAg(npP)Z is a potential microbicide agent against E. coli and C. albicans, and the OAg(n)(pT)Z for F. faecalis. [Figure: see text] ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1007/s40201-020-00501-z) contains supplementary material, which is available to authorized users.

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 (2–6 keV) 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.

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.

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.

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) = Aυn(p). The experimental results confirm, to a high degree of coincidence, the predictions made by these models.

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.

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.

This paper describes the design of a programmable stay-alone continuous radon monitoring system able to detect, count and store the amount of alpha particles with an energy of 5.49 MeV produced by the radioactive decay of environmental radon-222. It is included the electronic circuit design, the software development as well as the user interface and the hardware ensemble of all the system components.

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...

The design and implementation of a pulsed high voltage supply intended to the production and control of pulsed dielectric barrier discharges are reported. The instrumentation includes three independently built DC sources coupled to Flyback-like converters using three 1:50 high voltage transformers. The system is capable of supplying voltages up to 70 kV at a 100-2000 Hz repetition rate, delivering 1-500 ?s wide pulses. The system has been applied to the development of pulsed dielectric barrier discharges in a stainless steel coaxial reactor 30 cm long and with a 2.54 cm diameter. The inner nickel electrode diameter is 0.005 cm and is embedded in alumina. The discharges have been carried out in room pressure air. Discharges have been implemented. The discharge is made is a water environment for purposes of bacterial elimination.