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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]

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]

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: 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]

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: 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]

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]

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]