Collisional radiative (CR) models for molecular hydrogen are of high relevance for performing qualitative and quantitative analysis of excited-state population densities measured in plasmas or ...predicting the dependence of plasma emission on parameter variations. Although the development of such models for H2 started decades ago, major uncertainties still exist regarding the most important set of input parameters, namely the cross sections for electron-impact excitation. The deviations between cross sections from different datasets are particularly pronounced in the energy region close to the threshold energy, strongly increasing the uncertainty of CR models applied to low-temperature plasmas. This paper presents experimental validation of a set of newly calculated non ro-vibrationally resolved electron-impact cross sections calculated for the triplet system of H2 using the molecular convergent close-coupling method in the adiabatic-nuclei formulation. These cross sections are implemented into a CR model based on the flexible solver Yacora. A first comparison of CR calculations with the different datasets to experimentally-determined population densities is performed at a planar ICP discharge for varying pressure (between 1 and 10 Pa) and RF power (between 700 and 1100 W). For the experimentally-accessible electron temperature and density range (2.5-10 eV and 1.8-3.3 × 1016 m−3, respectively), very good agreement between the model and experiment is obtained using the new data set, in contrast to previously used cross sections.
Display omitted
•4-log10 MS2 viruses were inactivated in 150 s in this particular plasma setup.•A CCP plasma source is a good source of vacuum-ultraviolet radiation.•OH* radicals were determined as ...key oxidizing species produced by photolysis and O3.•Direct virus degradation by ozone was of secondary importance.•O3 degrades hydroxy terephthalic acid, while vacuum-ultraviolet radiation does not.
Water disinfection is a critical treatment step for removing harmful organisms from contaminated water sources. Vacuum ultra-violet (V-UV) radiation, generated by a low-pressure gaseous plasma discharge, consists of photons with high enough energy to break molecular bonds. In this work, we constructed and characterized a low-pressure capacitively coupled gaseous plasma and used it as a V-UV radiation source to inactivate MS2 bacteriophage, a surrogate for human enteric viruses. The treatment system allows for variation of gas composition inside the sample chamber and the modulation of V-UV radiation intensity. Both were used to separate the actual germicidal contribution of V-UV radiation from producing germicidal species by using virus inactivation to determine efficiency. OH* radical production was determined through the terephthalic acid chemical probe, which showed that when air was present in the sample chamber, it resulted in the highest OH* production and the best inactivation of MS2. Furthermore, we showcase that the OH* production rate was wavelength dependent and that ozone, generated by plasma treatment in the gas phase, leads to hydroxy terephthalic acid degradation, allowing us to determine better the actual OH* production rate with different treatment regimes. Lastly, by adding an OH* scavenger to the liquid, we were able to elucidate it as the primary inactivation agent in this setup while also providing evidence of its production in the bulk liquid by the transport and subsequent decomposition of the longer-lasting ozone molecule. This study demonstrates, for the first time, the applicability of low-pressure plasma radiation as a water treatment method.
The aim of this study was to evaluate the impact of oxygen and argon/oxygen low-pressure plasma on the shear bond strength (SBS) between dental PEEK compounds and veneering composites as a function ...of plasma process time.
Of an unfilled PEEK (“Juvora”) and two pigment powder filled PEEK compounds (“DC4420”, “DC4450”), 273 rectangular plates were prepared and polished up to 1200 grit. Afterwards the samples were sandblasted and randomly assigned to five different surface pre-treatment groups (1. No plasma (control); 2. O2 plasma for 3min; 3. O2 plasma for 35min; 4. Ar/O2 plasma for 3min; 5. Ar/O2 plasma for 35min). Surface roughness and water contact angles were recorded using three samples of each PEEK compound for each of the plasma treatment groups. An adhesive (visio.link, Bredent GmbH & Co KG, Senden, Germany) was applied onto the specimen surfaces and light cured. A mold was used to shape three different veneering composites (a) Vita VM LC, “Vita” (Vita Zahnfabrik, Bad Säckingen, Germany); (b) GC GRADIA, “Gradia” (GC Europe, Leuven, Belgium); (c) GC GRADIA DIRECT Flo, “Gradia Flo” (GC Europe, Leuven, Belgium)) into a cylindrical form on the sample surface before light curing. SBS was measured using a universal testing machine after 24h of incubation in distilled water at 37°C.
The two pigment filled PEEK compounds treated with O2 plasma and veneered with Gradia Flo showed the highest SBS values (34.92±6.55MPa and 34.2±1.87MPa) followed by the combination of the unfilled PEEK material with Gradia Flo (29.57±3.71MPa). The SBS values of the samples veneered with Gradia were lower, but not significantly so. The SBS values of the specimens with Vita were for the most part associated with significantly lower results.
A low-pressure plasma process using oxygen plasma for a duration of 35min, preceded by sandblasting, seems to be the most effective in increasing shear bond strength between veneering composites and PEEK materials.
Display omitted
•Endowing PVDF membrane surface with both photothermal and omniphobic properties.•Contribution of PDMS binder concentration to the efficiency of photothermal VMD.•Using low-pressure ...plasma polymerization to modify surface of PVDF membrane.
Given the scarcity of water and energy resources and their potential to escalate into future crises, water and energy have emerged as the paramount challenges of the present century. To address these challenges, simultaneously, a novel membrane distillation (MD) technique named photothermal MD (PMD) has come to the forefront in recent years. The PMD is rapidly advancing, particularly in the field of desalination, towards increasing the use of sustainable solar energy. In this work, the surface of poly(vinylidene fluoride) (PVDF) electrospun membrane was turned into a photothermal surface by binding graphene oxide (GO) nanosheets using a binder solution made of polydimethylsiloxane (PDMS) with different concentrations (0.1, 0.5, 1, 2, 3 wt%). Subsequently, the environmentally-friendly low-pressure plasma polymerization method was employed to polymerize perfluorodecyl acrylate (PFDA) monomers on the surface of coated electrospun membrane to achieve an omniphobic surface. In this regard, the contact angles of water, oil, and ethanol/water (70/30 v/v) solution on the surface of the coated membranes were measured to be 144°, 124.4°, and 120.8°, respectively. Compared to the uncoated electrospun membrane, the one coated with GO-containing binder solution with optimum PDMS concentration of 0.1 wt%, showed a significant increase in flux by 41 % at 1 sun irradiation during photothermal vacuum MD (PVMD). In the PVMD process, the conventional method of feed heating was substituted with membrane surface heating utilizing solar energy. Additionally, vacuum was employed to facilitate the passage of water vapor through the membrane pores. This increment was further highlighted by salt rejection remained constant at 99.9 %. It was also found that PDMS concentration in the GO-containing binder solution adversely affects the membrane efficiency, exhibiting a decreasing trend from 54.1 % to 17.5 % when PDMS concentration increases from 0.1 to 3 wt%. Additionally, the long-term performance assessment of the prepared membrane coated with the binder solution with optimum PDMS concentration of 0.1 wt% demonstrated its acceptable resistance against wetting by the NaCl aqueous solution (35 g/L) containing 0.3 mM sodium dodecyl sulfate (SDS).
To improve the high-temperature oxidation resistance of C/C composites, ZrB2–SiC (ZS) and ZrB2–SiC–TaSi2 (ZST) ultra-high temperature ceramics coatings were prepared on their surfaces using induction ...plasma spheroidization and low-pressure plasma spraying (LPPS). Ablation behaviors of the ZS and ZST coatings were evaluated at 1800°C, 2000°C, and 2200°C using the oxyacetylene flame, we found that the ZS coatings had good ablation resistance at 1800°C, but rapidly failed at 2000°C. Whereas, the ZST coating always performed good oxidation and ablation resistance at even 2000°C with a mass ablation rate of 4.68 × 10-5 g/s and a linear ablation rate of -1.63 × 10-5 mm s-1. The enhancement of the high temperature ablation resistance property was attributed to the introduction of the TaSi2, which improved the density of the coatings prepared by LPPS, reduced the volatilization of the glassy phase at high temperature, and enabled ZrO2 to form a dense oxide layer.
ZrB2-based composite coatings with addition of Al2TiO5 were prepared via very low-pressure plasma spraying using mechanically mixed powder of ZrB2 and Al2O3-40 wt%TiO2 (AT40). The ablation behavior ...of the composite coating was investigated using a high temperature plasma jet at a temperature of ∼2500oC. Results demonstrate the addition of AT40 improved the ablation resistance of the ZrB2 coatings at high temperatures. The coating with 17 vol%AT40 addition exhibited the lowest ablation rate, approximately 1.33 μm/s, which is only one-third of that of the pure ZrB2 coating. The added AT40 filled the pores between ZrO2 crystals during ablation, reducing oxygen penetration and lowering the ablation rate. However, excessive addition of AT40 hindered gaseous B2O3 release and thus led to large pore formation, impairing the protective effect. The ZrB2-AT40 coating is a promising candidate for high-temperature applications.
PDF
