Abstract The study on the inactivation of Escherichia coli (E. coli) bacteria in water flowing continuously in a treatment system based on two different reactors is presented. The bacteria inactivation is achieved in a water volume of 500 mL inoculated with an E. coli concentration of 1.45×103 bacteria/mL using combined treatment with ozone and ultraviolet (UV) radiation. Inoculated water firstly is introduced to cylindrical reactor supplied with ozone at a concentration of 1000-1100 ppm and, subsequently, transferred to a rectangular geometry reactor subjected to UV radiation with an energy per volume of 1.44 J/mL. Inactivation efficiency of E. coli bacteria in the water of 99.32% was attained in a total treatment time of 180 seconds.

Abstract Experimental investigation about methylene blue degradation in aqueous solution applying several Advanced Oxidation Processes such as O3, O3/H2O2, O3/UV and O3/UV/H2O2 was accomplished. Methylene blue treatment consisted in evaluating the degradation of an initial concentration of 22 ppm in 500 ml of aqueous solution. The contaminant degradation efficiencies were analyzed considering parameters such as: treatment time, three different pH values for the solution and O3 and H2O2 as oxidizing reagents. The discoloration of the samples was examined throughout the experimental each 10 minutes. Using O3/UV/H2O2 (10 ppm) with an initial 7 pH and a treatment time of 60 minutes the highest degradation efficiency of 98% was achieved.

The determination of the different radiation fields in an electron accelerator requires the use of selected radiation detectors, in this work we describe the experimental considerations on the determination of the intensity of electrons and X-rays generated by bremsstrahlung in an experimental electron accelerator covering the energy range from 80 keV to 485 keV. A lithium- drifted silicon detector, a high-purity germanium detector, a scintillation detector and a PIN diode were used in the experiments. Spectroscopic measurements allowed us to verify the terminal voltage of the accelerator. The PIN photodiode can measure the intensity of X-rays produced, with this information, we could determine its relationship with both the electron beam current and the accelerating voltage of the accelerator.

Pure nitrogen, 30% argon/70% nitrogen, 50% argon/50% nitrogen, 70% argon/30% nitrogen plasma immersion ion implantation (PIII) processes onto aluminium samples has been performed at 2 to 6 kV negative bias and 50 to 150 us pulse widths, the sample temperature being established at 400 °C. Incident fluencies of ~10(18) atoms/cm² were used to investigate the diffusion behaviour and AlN phase formation in the samples. X-ray diffraction (XRD) shows the formation of the cubic phase of AlN with both pure nitrogen and all the mixtures whereas the hexagonal phase becomes apparent only in the 50% mixture and in pure nitrogen. The characteristic peak of AlN has also been determined by Raman spectroscopy. The microhardness was found to be always maximal with the 50% nitrogen 50% argon mixture.

This study reports the surface modification of AISI 304 stainless steel by applying nitrogen ion implantation by low energy plasma at different temperatures (380°C, 400°C, 440°C). The temperature of the samples was adjusted by varying the implantation pulse width while keeping the voltage constant at 1.5 kV. Microstructure and phase characterization were carried out by scanning electronic microscopy (SEM) and X-ray diffractometry (XRD) respectively. The surface hardness was determined by Knoop measurements, and the results show that the treatment increases up to two times the substrate hardness value. Additionally, it was found a direct dependence between the substrate temperature and the nitrided layer thickness. X-ray diffraction patterns indicate the shift of the peaks of the treated samples to lower angles than those of the untreated samples, which is a clear signature of expanded austenite.

Samples of pure Titanium were treated by means a PIII process using a dense DC glow discharge with different mixtures of nitrogen-oxygen and oxygen pure. The surface of treated samples was analyzed by means of different techniques such as X-ray diffractometry, Scanning Electron Microscope, Vickers Microhardness tester and profilometer. We conclude that the modified surface is formed by TiN0.26 diffused into TiO2 in rutile phase, forming a uniform layer up to 10 μm in thickness and whose resultant microhardness is almost five times greater than that of untreated titanium. Some control over the superficial parameters is taken by varying the proportion of nitrogen-oxygen at a pressure of 1x10-2 Torr (~1.33 Pa), obtaining a thicker layer, a harder surface or a reduced roughness. The identified phases have biocompatible properties, which provide interest in the bioengineering field.

Some recent results concerning the synthesis of carbon nanostructures in a thermal plasma generating by a plasma torch are presented. Several tests were carried out in different operational conditions. The plasma was formed with argon and different gas mixtures of argon-acetylene or argon-methane to which some catalyst materials (ferrocene and cerium oxide) were added. These catalysts were introduced into the plasma in a solid (powder) or/and a gaseous state. Their feeding rate into the plasma jet was fixed along with some other operating conditions such as plasma power, gas flow rate and reactor pressure. The principal main feature observed was a short reaction time so that each test lasted for no longer than 5 minutes. The solid products obtained were collected and prepared for following analyses. The products were examined using XRD and TEM techniques in order to characterize the morphological structure of their samples. The spatial distribution of temperature in the plasma was evaluated by in-situ emission spectroscopy. The self-absorption was taken into account by simulating an integrated radiation in relation to the Swan band d³pig -> a³piu(0,0), emitted by the C2 radical. Also, the exhaust gases were characterized by gas chromatography during each test.

One alternative application in the decomposition and destruction of volatile organic compounds (VOCs) by a silent plasma dielectric barrier discharge (DBD) has been successfully accomplished. For this purpose, we have designed and constructed two pairs of cells, of rectangular and circular geometries, 333.96 cm³ each cell, and a similar second pair of 62.25 cm³ each one. Resonant inverters for low (3.3 kHz) and high (100 kHz) frequencies were also designed and applied to these cells. The specification of the main physical parameters of each cell contemplates: i) a first order degradation ratio of the compound, and ii) air breakdown at atmospheric pressure as a function of the carrying gas. The power consumed by the cells during the discharges was computed both theoretically and experimentally by Manley's method. The equipment was applied to the degradation of toluene, which has been degraded by an oxidation process in air-oxygen and argon-oxygen gas mixtures at atmospheric pressure within the cells. The destruction efficiency was measured as a function of the initial concentration. When air is used as an oxidant, a clear formation of solid products on the walls of dielectric glass plates has been observed, such deposits being polymeric in nature. These deposits seem to be responsible for a decline in the degradation efficiency of the treated compounds.

Plasma immersion ion implantation (PIII) of stainless steels with nitrogen has been successfully used for surface hardening purposes. This process has been carried out inside a toroidal discharge chamber in a DC/RF plasma. The RF plasma was created by one antenna located inside the chamber, diametrically opposite to the DC electrode. The latter is polarized with 1 kV and then the discharge is controlled by varying the gas pressure before the RF signal is applied. The main plasma parameters were established by means of double electric probes yielding electron temperature values within 0.5-1.5 eV and density values within 1.5×10(15) to 4×10(15) m-3 for the DC case while 1.5-3.0 eV and 7×10(14) to 3×10(15) m-3 were reached with RF assisted DC. We present in this work the experimental results obtained from a PIII process applied to AISI 304 stainless steel plates. The outcome shows that the Vickers hardness has been incremented according to the gas pressure within the 1×10-1 to 1×10-3 mbar range. The treated plates were analyzed by scanning electron microscopy (SEM) and the results point to an increased percentage of nitrogen, around 20%. By means of x-ray diffractometry (XRD) the gamma expanded phase and compounds such as Fe3NiN, Ni4N, FeNiN and Fe3N were determined.