The application of gas discharge plasmas has assumed an important place in many manufacturing processes. Plasma methods contribute significantly to the economic prosperity of industrialized societies. However, plasma is mainly an enabling method and therefore its role remains often hidden. Hence the success of plasma technologies is described for different examples and commercial areas. From these examples and emerging applications, the potential of plasma technologies is discussed. Economic trends are anticipated together with research needs. The community of plasma scientists strongly believes that more exciting advances will continue to foster innovations and discoveries in the first decades of the 21st century, if research and education will be properly funded and sustained by public bodies and industrial investors.
Summary form only given. A direct current atmospheric pressure cold plasma jet was used to inactivate Staphylococcus aureus (S. aureus) suspended in a liquid. Three types of gases, pure argon (99.999%), argon with 2% oxygen, and argon with 2% oxygen and 10% nitrogen were used as operating gases respectively. The inactivation efficacies for the plasma jets operating in the three gases decrease from Ar/O 2 (2%) to Ar/O 2 (2%)/N 2 (10%) to pure Ar. Optical emission spectroscopy (OES), electron spin resonance (ESR) spectroscopy, high performance liquid chromatography (HPLC), and atomic absorption spectrophotometry (AAS) were employed to identify and monitor the reactive species in the plasma-liquid system for the three operating gases and revealed the presence of O, 1 O 2 , OH, NO, H 2 O 2 , O 3 , and NO 3- /NO 2- as well as Cu (Cu + /Cu2 + ). The S. aureus inactivation results indicate that atomic oxygen is the key inactivation agent here, while other species play a lesser role in the inactivation progress studied here.
The purpose of this study is to evaluate the changes in dental enamel (morphology, elemental composition, microhardness, and roughness) after applying hydrogen peroxide in conjunction with a nonthermal plasma to bleach the teeth. Extracted human teeth were randomly placed in six groups. Two control groups (one group with no bleaching agent and no plasma treatment of the teeth and another one with only hydrogen peroxide as the bleaching agent) and four plasma groups (receiving hydrogen peroxide of varying concentrations 6%, 15%, 25%, and 35%, in conjunction with a plasma treatment) were prepared. The surface morphology before and after treatment was assessed using a scanning electron microscope (SEM), and the change in the elemental composition was analyzed by an energy-dispersive X-ray spectroscopy system. A total of 36 extracted teeth were used to evaluate the change in enamel microhardness and surface roughness. The use of hydrogen peroxide as a bleaching agent, even in the absence of plasma exposure, causes various etching patterns that are attributable to demineralization during the treatment process. These patterns are more pronounced as the hydrogen peroxide concentration increases. The surface roughness tests confirmed the findings from the SEM analysis. We only found minor essentially insignificant changes in the elemental composition of the enamel and in the surface microhardness as a result of the treatment using hydrogen peroxide and a cold plasma. The use of a cold plasma in conjunction with hydrogen peroxide of varying concentrations in tooth bleaching causes minor changes in the tooth enamel changes that are comparable to those resulting from the standard treatment using 35 % hydrogen peroxide gel without a plasma.
Summary form only given. Recently, a few attempts have been reported to inactivate bacteria in aqueous environments. Although effective inactivation of bacteria in their vegetative state (suspended in water) by non-thermal plasmas in or near the water has been reported, few studies have observed effective inactivation of bacterial spores. In this study, a direct-current, cold plasma microjet (PMJ) with atmospheric air as the working gas, sustained in a quasi-steady gas cavity in water, was used to inactivate Bacillus subtilis spores (suspended in water). The PMJ was operated at an air at a flow rate of ~5 slm and a current of 30 mA. The overall pH and temperature of the liquid were observed to change from 7.5 to a steady-state value of 3.4 and from 25° C to 40° C, respectively. The concentrations of NO 2- , NO 3- and H 2 O 2 were observed to change from 0 to tens of ppm after a 20 min PMJ treatment. Water (without spore suspension) treated with plasma for 20 min was immediately applied to B. subtilis spores to evaluate the effect of long-lived reactive species in water (such as O3) on the inactivation. Other reactive oxygen species and reactive nitrogen species (ROS/RNS), such as OH, O 2- and ONOO - were detected by Electron Spin Resonance spectroscopy.
The 44 papers in this special issue address unresolved basic science issues related to atmospheric pressure plasmas and also show the wide range of their practical applications.
This entry presents a brief overview of the use of microplasmas in a broad range of environmental applications such as ozone generation and pollution remediation including electrostatic precipitators and biological applications (decontamination and sterilization of individual microorganisms as well as biofilms).
The semiclassical Deutsch-Märk (DM) formalism was used to calculate absolute cross sections for the electron-impact ionization of metastable atoms such as metastable rare-gas atoms and metastable mercury and cadmium atoms from threshold to 200 eV. Systematic trends in the calculated cross section data are discussed and a comparison is made with available experimental data and with other calculations. Specifically, we calculated separately the contributions to the ionization cross sections arising from the removal of the single excited electron in the outermost subshell and the removal of the lower-lying inner-shell electrons.
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