Pressure Air Plasma Research Articles

The conceptual design of high temporal resolution HCN interferometry for atmospheric pressure air plasmas

A heterodyne interferometer operating at the frequency f = 890 GHz has been designed for measuring the electron density of atmospheric pressure air plasmas, it's density range is from 1015 to 3×1019 m−3 and the pressure range is from 1 Pa to 20 kPa. The system is configured as a Mach\ obreakdash-Zehnder type interferometer. The light source is hydrogen cyanide (HCN) laser with a wavelength of 337 μm, which is suitable for the high density area, 1018 to 3×1019 m−3, of atmospheric pressure air plasmas. The HCN laser power is up to 100 mW. The intermediate frequency, shifted by 500 kHz, is generated by the Doppler shift with a high speed rotating grating (HSRG), which is installed in a vacuum vessel with gas pressure less than 1 Pa. With the HSRG, the temporal resolution of the HCN interferometry can reach to 2 μs. Beam path analysis based on Gaussian optics is used in the design of the optical system. The VDI planar-diode Integrated Conical Horn Fundamental Mixers optimized for high sensitivity—typical RF responsivity is around 900 V/W —will be used in the HCN interferometry. The detailed optical design and opto-mechanical design for the HCN interferometry are presented.

The generation and transport of reactive nitrogen species from a low temperature atmospheric pressure air plasma source.

The reactive chemical species generated by non-equilibrium plasma under atmospheric pressure conditions are key enablers for many emerging applications spanning the fields of biomedicine, manufacturing and agriculture. Despite showing great application potential, insight in to the underpinning reactive species generation and transport mechanisms remains scarce. This contribution focuses on the spatiotemporal behaviour of reactive nitrogen species (RNS) created and transported by an atmospheric pressure air surface barrier discharge (SBD) using both laser induced fluorescence and particle imaging velocimetry measurements combined with experimentally validated numerical modelling. It was observed that highly reactive species such as N are confined to the discharge region while less reactive species such as NO, NO2 and N2O closely followed the induced flow. The concentration of key RNS was found to be in the 10-100 ppm range at a position of 25 mm downstream of the discharge region. A close agreement between the experimental and computational results was achieved and the findings provide a valuable insight in to the role of electrohydrodynamic forces in dictating the spatiotemporal distribution of reactive chemical species beyond the plasma generation region, which is ultimately a key contributor towards downstream treatment uniformity and application efficacy.

On Hemostasis of Cold Atmospheric Air Plasma

The efficacy and mechanism of a cold atmospheric-pressure air plasma (CAAP), which carries abundant atomic oxygen (OI), on blood coagulation are studied. The tests on sodium citrate mixed blood-droplet samples show that 1) The heat delivered by the CAAP has no impact on the observed clot formation, 2) Plasma effluent activates platelets to promote coagulation state and cascade, and 3) The degree of clotting increases with the OI flux delivered by the CAAP. The full clotting time is shortened from about 25 minutes of the natural clotting time to about 16 s of the CAAP treatment time. The tests on smeared blood samples show that the reduction of the platelet count and the increase of RBC count are proportional to the applied OI flux. In vivo tests, using swine as nimal model, swift hemostasis of large and deep cut wounds on the back by the CAAP treatment was demonstrated. A cut artery was sealed completely with 25 s treatment. The pressure applied by a finger on the cut artery could be removed immediately after the treatment and there was no re-bleed. Based on the in vitro test results and the animal model trials, CAAP coagulation mechanism is presented.

Redox performance of Na-modified Fe2O3/Al2O3 with syngas as reducing agent in chemical looping combustion process

The redox performances of 1–10 wt% Na-modified Fe2O3/Al2O3 oxygen carrier from seawater were investigated using syngas/air as reactive gases in the thermogravimetric analyzer (TGA) and lab-scaled semi-fluidized bed reactor (semi-FzBR). NaNO3(aq) as the source of sodium dopants to prepare Na-contained solution was implemented by an air atmospheric pressure plasma jet (Air-APPJ) process, which can increase the feasibility of seawater. For the prepared samples, the materials properties, including crystalline phases, surface morphologies, surface areas, and attrition loss performances were well correlated with the Na contents. The results indicated that the poor reduction kinetics and attrition resistance were obtained with the Na adjunction over 5 wt%, attributing to the sintering issue on excessive phases of Na2(Al, Fe)12O19 and Na(Al, Fe)O2 solid solution in the samples. Therefore, the slight incorporation of Na content in the Fe2O3/Al2O3 samples which improved the reduction rate was proved as the candidate oxygen carriers. Particularly, the Na content with 1 wt% in Fe2O3/Al2O3 sample (Na1FA32) can significantly promote the reduction behavior, thermal stability, and attrition resistance as compared to the raw Fe2O3/Al2O3 oxygen carrier. It is environmentally beneficial to use the Na1FA32 as oxygen carrier in a practical chemical looping combustion process.

A novel cold atmospheric pressure air plasma jet for peri-implantitis treatment: An in vitro study.

Peri-implantitis is difficult to treat in clinical settings; this is not only because it is a site-specific infectious disease but also because it impedes osseointegration. In this study, a novel cold atmospheric pressure air plasma jet (CAPAJ) was applied to study the treatment of peri-implantitis in vitro. CAPAJ treated the samples for 2, 4 and 6 min, respectively. To evaluate the titanium surface characteristics, the surface elemental composition (X-ray photoelectron spectroscopy [XPS]), roughness and hydrophilicity were evaluated in each group. Concurrently, the sterilization and osseointegration effect of CAPAJ were also examined. Results revealed that after CAPAJ modification, roughness and hydrophilicity of titanium surfaces were significantly increased. Moreover, XPS results demonstrated that the C1s peak was reduced and N1s and O1s peaks were obviously improved. More importantly, CAPAJ showed favorable sterilization and bone formation effects. CAPAJ seemed a simpler and more efficient strategy for the peri-implantitis treatment.

Liquid Phase Reactive Species Formation by Atmospheric Pressure Air Plasma Jet

Liquid Phase Reactive Species Formation by Atmospheric Pressure Air Plasma Jet

Carbon-free SiOx ultrathin film using atmospheric pressure plasma jet for enhancing the corrosion resistance of magnesium alloys

This study describes the use of tetraethylorthosilicate (TEOS) as the precursor to deposit carbon-free silica (SiO2) dense film as the anti-corrosion layer on the surface of AZ91D magnesium alloys using an air atmospheric pressure plasma jet (APPJ). From the contact angle measurements, APPJ-deposited silica film on AZ91D represents a more hydrophobic property with a lower total surface free energy of 31.3 mN/m. XPS depth profile analyses revealed the chemical compositions (O and Si) were uniformly distributed through the bulk of the deposited films with a thickness of 207 nm, which also comprises of carbon-free SiO2 ultrathin films. The electrochemical impedance spectroscopy (EIS) measurements and corrosion morphologies of 14-day immersion test of deposited films and AZ91D samples in 3.5 wt % NaCl solution are also investigated. The results indicate ultrathin silica coating not only alter the surface property, but also improve the corrosion resistance of AZ91D magnesium alloys.

A cost- and time-saving strategy of spraying TiO2 self-cleaning coatings in tubular substrates by air cold plasma

In this study, using an atmospheric pressure air plasma jet generated by a dielectric barrier structure with hollow electrodes (HEDBS), we developed an ultrafast process for spraying TiO2 self-cleaning films inside tubular substrates. Importantly, SEM images showed that the TiO2 particles were dispersed evenly in the tubular substrates. Furthermore, Raman and XRD pattern indicated the anatase structure of the HEDBS-spayed TiO2 coating after heating at 270°C. Further results of the self cleaning test suggested that the proposed cost- and time-saving HEDBS approach with air working gas could provide a feasible way for synthesizing thin TiO2 nanofilms.

Atmospheric pressure air plasma treatment of glass substrates for improved silver/glass adhesion in solar mirrors

Atmospheric pressure air plasma treatment was applied to glass substrates to improve the adhesion of the reflective silver layer of mirrors used in solar power systems. This treatment attempts to prevent problems related to the detachment of this layer that affect its energy performance. Untreated and plasma treated glass substrates were subjected to a spray coating process to fabricate mirrors. Chemical characterization by X-ray Photoelectron Spectroscopy (XPS) and measurements of the water contact angle (WCA) were undertaken on the glass substrates before the plating process. The reflectivity of the mirrors was studied by spectrophotometry in the wavelength range of 280–2500nm, and the adhesion between the glass substrates and the silver layers was measured by pull-off tests. In order to determine the relationship between the parameters of the plasma treatment and the adhesion and reflectivity of the mirrors, different combinations of treatment speeds and gap distances between the glass substrates and the plasma nozzle were used. It was observed that the plasma treatment has a cleaning effect and forms oxygen-based functional groups that promote the hydrophilicity of the glass substrates. This double effect resulted in improved adhesion of the silver layer to the plasma treated substrates, with no significant loss of solar reflectance of the mirrors. The plasma treatment with the lowest gap distance (2mm) and the lowest speed (1m/min) achieved the best results in this work. It brought an improvement of 85.8% in the breaking strength of the untreated glass mirror and no significant variation in the solar reflectance in as-fabricated conditions. After accelerated aging, it maintained an improvement of 27.2% in the breaking strength and showed higher solar reflectance than the untreated glass mirror.

In Situ Regeneration of Au Nanocatalysts by Atmospheric-Pressure Air Plasma: Regeneration Characteristics of Square-Wave Pulsed Plasma

Atmospheric-pressure air plasma, powered by alternating current (AC) sine-wave high voltage, can in-situ regenerate deactivated Au nanocatalysts during CO oxidation, but it needs high-humidity air as the discharge gas. To overcome the limitation on humidity for in-situ regeneration of air plasma, a square-wave pulsed plasma is applied in this work. Differently from the AC plasma, the pulsed plasma exhibits excellent regeneration performance at any humidity. Further, surface carbonate decomposition, nitrogen oxides poisoning species and electric discharge of the pulsed plasma regeneration are investigated. For the pulsed plasma regeneration at any humidity, the evolution of CO2 concentration with the regeneration time almost keeps the same profile, featuring zero-order kinetics for the carbonate decomposition; on the other hand, whether in the gas phase or on the catalyst surface, there are no formation of poisoning nitrogen oxides. The pulsed plasma at any humidity has the powerful ability in carbonate decomposition and simultaneously prevents the formation of poisoning nitrogen oxides, which is ascribed to its highly centralized energy deposition with high instantaneous power and long interval of instantaneous power. For practical application, normal air is also confirmed to be qualified for the pulsed plasma regeneration.

Influence of gas flow velocity on the transport of chemical species in an atmospheric pressure air plasma discharge

This paper reports on a numerical study of the transport of reactive chemical species generated in an atmospheric-pressure air plasma discharge under the influence of a high velocity flowing gas. Using a 1D air plasma model, it is shown that the reactive species transported downstream of the discharge region can be categorized into three distinct groups based on their spatial distribution: (i) decaying downstream species, (ii) increasing downstream species and (iii) variable density species, where the density is a function of both spatial position and gas flow velocity. It is demonstrated that the gas flow velocity influences the dominant chemical reactions downstream of the discharge region, noticeably altering the composition of several key reactive chemical species transported to a given downstream location. As many emerging applications of atmospheric pressure plasma are driven by the flux of reactive chemical species, this study highlights the importance of gas flow velocity, not only as a means to enhance mass transport but also as a means to manipulate the very nature of the reactive plasma chemistry arriving at a given location.

Non-thermal air plasma promotes the healing of acute skin wounds in rats

Non-thermal plasma (NTP) has nonspecific antibacterial effects, and can be applied as an effective tool for the treatment of chronic wounds and other skin pathologies. In this study we analysed the effect of NTP on the healing of the full-thickness acute skin wound model in rats. We utilised a single jet NTP system generating atmospheric pressure air plasma, with ion volume density 5 · 1017 m−3 and gas temperature 30–35 °C. The skin wounds were exposed to three daily plasma treatments for 1 or 2 minutes and were evaluated 3, 7 and 14 days after the wounding by histological and gene expression analysis. NTP treatment significantly enhanced epithelization and wound contraction on day 7 when compared to the untreated wounds. Macrophage infiltration into the wound area was not affected by the NTP treatment. Gene expression analysis did not indicate an increased inflammatory reaction or a disruption of the wound healing process; transient enhancement of inflammatory marker upregulation was found after NTP treatment on day 7. In summary, NTP treatment had improved the healing efficacy of acute skin wounds without noticeable side effects and concomitant activation of pro-inflammatory signalling. The obtained results highlight the favourability of plasma applications for wound therapy in clinics.

Surface Modification of Aramid Fiber III by the Atmospheric-Pressure Air Plasma Treatment

Aramid fiber III has been treated by plasma treatment on different atmosphere gas to enhance the adhesive force between Aramid fiber III and epoxy matrix. The results of contact angle and SEM indicate that the obvious corrosion appear in the surface of aramid fiber III after plasma treatment. The yarn pull-out method was used to evaluate the effect of surface modification. The contact angle of original aramid fiber III is 65.9 o, and after treated the contact angle is declined to 62.2 o. The evaluation results show the tensile strength and NOL ILSS of treated Aramid fiber III/epoxy composite increased by about 10%. In summary, the effect of plasma treatment is obvious and has potential industry application.

A facile method for sodium-modified Fe2O3/Al2O3 oxygen carrier by an air atmospheric pressure plasma jet for chemical looping combustion process

The use of seawater as catalytic agents for hematite (Fe2O3) as oxygen carrier in chemical looping combustion process is attractive, because of its abundance and low cost. Unfortunately, seawater itself with major NaCl compound under reactive species accompanying the volatilization of chlorine-containing gases probably lead to the corrosion on reactors during the combustion process. In this study, the feasibility evaluation of sodium dopants extracted from seawater as an effective catalytic agent via an air atmospheric pressure plasma jet (Air-APPJ) is performed, and as such it is combined with Fe2O3/Al2O3 to assess any possible enhancement on the reduction kinetics. The sodium-contained solutions, NaNO3(aq) and NaCl(aq), as precursors are used to prepare the sodium dopants due to the evaporation-decomposition of water and dissolved salts via plasma discharge reaction. The sodium-modified Fe2O3/Al2O3 oxygen carrier can significantly promote the efficiency of the carbon capture efficiency and CO2 yield. Especially for the NaCl(aq) as precursor in an Air-APPJ system, the high carbon capture efficiency, CO2 molar fraction and CO2 yield around 0.96, 0.95 and 0.91 after fifty redox cycle for the sodium-modified Fe2O3/Al2O3 oxygen carrier are achieved. It can be anticipated that the sodium-modified Fe2O3/Al2O3 from seawater by an Air-APPJ system as an oxygen carrier candidate in a reversible CLC process would be notably attractive.

Cold atmospheric-pressure air plasma treatment of C6 glioma cells: effects of reactive oxygen species in the medium produced by the plasma on cell death

An atmospheric-pressure air plasma is employed to treat C6 glioma cells in vitro. To elucidate on the mechanism causing cell death and role of reactive species (RS) in the medium produced by the plasma, the concentration of the long-lived RS such as hydrogen peroxide, nitrate, and ozone in the plasma-treated liquid (phosphate-buffered saline solution) is measured. When vitamin C is added to the medium as a ROS quencher, the viability of C6 glioma cells after the plasma treatment is different from that without vitamin C. The results demonstrate that reactive oxygen species (ROS) such as H2O2, and O3 constitute the main factors for inactivation of C6 glioma cells and the reactive nitrogen species (RNS) may only play an auxiliary role in cell death.

Fast and Low-Temperature (70 °C) Mineralization of Inkjet Printed Mesoporous TiO2 Photoanodes Using Ambient Air Plasma.

Hybrid mesoporous titania/silica electron-generating and transporting layers were prepared using wet-coating with a dispersion consisting of prefabricated titania nanoparticles and a methyl-silica binder. Titania/methyl-silica wet layers were deposited by inkjet printing and further mineralized by low-temperature atmospheric-pressure air plasma using diffuse coplanar surface barrier discharge (DCSBD) to form a titania/silica hybrid nanocomposite coating. Morphological analysis performed by scanning electron microscopy revealed no damage to the titania nanoparticles and chemical analysis performed by X-ray photoelectron spectroscopy disclosed a rapid decrease in carbon and increase in oxygen, indicating the oxidation effect of the plasma. The coatings were further electrochemically investigated with linear sweep voltammetry and chronoamperometry. The magnitude of photocurrent and photocatalytic activity were found to increase significantly with the plasma exposure on the order of 10s of seconds. The results obtained demonstrate the potential of DCSBD ambient air plasma for fast and low-temperature mineralization of titania mesoporous coatings.

Dynamics and Structure of Nonthermal Atmospheric-Pressure Air Plasma Jets: Experiment and Simulation

Results of experimental and computational study of the dynamics and structure of atmospheric-pressure air plasma jets formed by barrier discharge in a thin dielectric tube are presented. Formation of plasma bullet-guided streamers, moving along the jet with velocity varying in the range (1–3) $\times 10^{{\mathrm {7}}}$ cm $\text{s}^{{\mathrm {-1}}}$ , is observed. Simulation, for conditions of the experiment, gives the streamer radius, velocity, and propagation length in reasonable agreement with the experimental data.

Infrared spectroscopic measurements of carbon monoxide within a high temperature ablative boundary layer

Theoretical studies have indicated that the formation of carbon monoxide within a high temperature ablative boundary layer can significantly alter the afterbody radiative heat transfer to the surface of a reentry capsule. This paper represents a first attempt to experimentally measure the concentration of carbon monoxide within the high temperature boundary layer surrounding an ablative material exposed to an atmospheric pressure air plasma. A plasma torch facility was used to produce the high temperature flow and a sample of ASTERM ablative material was inserted into the flow. At the stagnation point, the heat flux to the surface was estimated at 8 MW m−2 and the surface temperature at 2900 ± 100 K. Both emission and absorption spectroscopy techniques were used to measure the distribution of carbon monoxide within the flow. Emission spectroscopy yielded better signal-to-noise measurements, but the absorption spectroscopy measurements were used to validate emission measurements. In the cases examined, both emission and absorption measurements were consistent and in agreement with one another. Estimates of carbon monoxide temperature and mole fraction were deduced from the spectra taken within the boundary layer downstream of the stagnation point. No carbon monoxide was observed at the stagnation point. These measurements provide a test case for numerical simulations of plasma-ablator interactions.

Effects of Atmospheric-Pressure Nonthermal Nitrogen and Air Plasma on Bacteria Inactivation

An atmospheric-pressure nonthermal plasma jet operated with nitrogen and air is used to investigate the inactivation of bacterium P. aeruginosa. To better understand the bactericidal efficiency of the reactive species (RS) with a different lifetime, direct and indirect treatments are used to inactivate the bacteria with different initial bacteria numbers and Petri dishes. No obvious difference is observed between the nitrogen and air plasmas in the direct treatment, but the air plasma is more efficient in the indirect treatment due to more O3 and NO. The direct treatment is much more efficient than the indirect one because of the participation of charged particles and RS, such as N2(A), N (4S), O(1S), and O(3P). However, the indirect treatment covers a larger area on account of the more diffusion of the long-lived RS O3 and NO. Our results show that the plasma jet is more suitable for wound therapy although the treated area is small.

Open air plasma deposited antimicrobial SiOx/TiOx composite films for biomedical applications

Abstract Open air atmospheric pressure plasma jet (APPJ) enhanced chemical vapour deposition process was used to deposit biocompatible SiOx/TiOx composite coatings. The as deposited films are hydrophilic and show visible light induced photocatalytic effect, which is a consequence of the formation of defects in the TiOx structure due to the plasma process. This photocatalytic effect was verified by the demonstration of an antimicrobial effect under visible light on E. coli as well as by degradation of Rhodamine B. The films are non-cytotoxic as shown by the cytocompatibility tests. The films are conductive to cell growth and are stable in DMEM and isopropanol. The structural evaluation using SEM, EDS and XPS shows a dispersion of TiOx phase in a SiOxCyHz matrix. These analyses were used to correlate the structure-property relationship of the composite coating.