Plasma Gas Temperature Research Articles

Modelling the Plasma Jet in Multi-Arc Plasma Spraying

Particle in-flight characteristics in atmospheric plasma spraying process are determined by impulse and heat energy transferred between the plasma jet and injected powder particles. One of the important factors for the quality of the plasma-sprayed coatings is thus the distribution of plasma gas temperatures and velocities in plasma jet. Plasma jets generated by conventional single-arc plasma spraying systems and their interaction with powder particles were subject matter of intensive research. However, this does not apply to plasma jets generated by means of multi-arc plasma spraying systems yet. In this study, a numerical model has been developed which is designated to dealing with the flow characteristics of the plasma jet generated by means of a three-cathode spraying system. The upstream flow conditions, which were calculated using a priori conducted plasma generator simulations, have been coupled to the plasma jet simulations. The significances of the relevant numerical assumptions and aspects of the models are analyzed. The focus is placed on to the turbulence and diffusion/demixing modelling. A critical evaluation of the prediction power of the models is conducted by comparing the numerical results to the experimental results determined by means of emission spectroscopic computed tomography. It is evident that the numerical models exhibit a good accuracy for their intended use.

Synthesis of flat sticky hydrophobic carbon diamond-like films using atmospheric pressure Ar/CH4 dielectric barrier discharge

An Ar/CH4 atmospheric pressure dielectric barrier discharge (AP-DBD) was used to synthesize sticky hydrophobic diamond-like carbon (DLC) films on glass surface. The film is formed with plasma treatment duration shorter than 30 s, and water contact angles larger than 90° together with contact angle hysteresis larger than 10° can be achieved. According to Fourier transform infrared spectroscopy and atomic force microscopy analysis, hydrocarbon functional groups are created on the glass substrate, producing coatings with low surface energy (∼35 mJ m−2) with no modification of the surface roughness. To infer the plasma processes leading to the formation of low energy DLC surfaces, optical emission spectroscopy was used. From the results, a direct relationship between the CH species present in the plasma and the carbon concentration in the hydrophobic layer was found, which suggests that the CH species are the precursors of DLC film growth. Additionally, the plasma gas temperature was measured to be below 350 K which highlights the suitability of using AP-DBD to treat thermo-sensitive surfaces.

Optical characteristics of the filamentary and diffuse modes in surface dielectric barrier discharge

Surface dielectric barrier discharge (DBD) plasmas generally exhibits filamentary and diffuse discharges at atmospheric air. The focus of this investigation is on the different optical characteristics and quantitative research about morphological features of two discharge modes. The temporally and spatially resolved characteristics of discharge phenomenon together with the gas temperature are presented with microsecond time scale. Discharge area is estimated by the sum of pixels that equal to “1” in MATLAB software. The formation of diffuse plasma mainly depends on an increase of the ionization coefficient and a creation of sufficient seed electrons by the Penning effect at low electric fields. Accordingly, experimental measurements show that diffuse discharge during the negative half cycle has good uniformity and stability compared with filamentary discharge during the positive half cycle. The rotational temperatures of plasma are determined by comparing the experimental spectra with the simulated spectra that have been investigated. The plasma gas temperature keeps almost constant in the filamentary discharge phase and subsequently increased by about 115K during the diffuse discharge. In addition, it is shown to be nearly identical in the axial direction. Non-uniform temperature distribution can be observed in the radial direction with large fluctuations. The plasma length is demonstrated almost the same between two discharge modes.

Needle-array to Plate DBD Plasma Using Sine AC and Nanosecond Pulse Excitations for Purpose of Improving Indoor Air Quality.

In this study, needle-array to plate electrode configuration was employed to generate an atmospheric air diffuse discharge using both nanosecond pulse and sine AC voltage as excitation voltage for the purpose of improving indoor air quality. Different types of voltage sources and electrode configurations are employed to optimize electrical field distribution and improve discharge stability. Discharge images, electrical characteristics, optical emission spectra, and plasma gas temperatures in both sine AC discharge and nanosecond pulse discharge were compared and the discharge stability during long operating time were discussed. Compared with the discharge excited by sine AC voltage, the nanosecond pulsed discharge is more homogenous and stable, besides, the plasma gas temperature of nanosecond pulse discharge is much lower. Using packed-bed structure, where γ- Al2O3 pellets are filled in the electrode gap, has obvious efficacy in the production of homogenous discharge. Furthermore, both sine AC discharge and nanosecond pulse discharge were used for removing formaldehyde from flowing air. It shows that nanosecond pulse discharge has a significant advantage in energy cost. And the main physiochemical processes for the generation of active species and the degradation of formaldehyde were discussed.

Analysis of Electrical Discharge Plasma in a Gas‐Liquid Flow Reactor Using Optical Emission Spectroscopy and the Formation of Hydrogen Peroxide

Optical emission spectroscopy was used to characterize an electrical discharge plasma reactor with a liquid H2O film contacting different carrier gases. The plasma gas temperatures for Ar, He, and 1% N2 in Ar were 1000–1200 K and did not vary significantly with liquid flow rate. Increasing solution conductivity by adding KCl to deionized water in the Ar case lowered the temperature by 13%, increased the discharge power and lowered the H2O2 formation rates. The temperature was highest in the case of air (2400 K), and in the case of Ar the temperature increased with the addition of O2. The temperatures for this reactor are comparable to previous studies with discharges in humid gases, while the effects of liquid conductivity were similar to those reported with direct discharge in the liquid phase.

Production of the low-molecular-weight chitin and chitosan forms in electron-beam plasma

The degradation of chitin and chitosans of different molecular weights stimulated by electronbeam plasmas of different gases has been experimentally studied. Biologically active water-soluble lowmolecular-weight chitooligosaccharides are formed as a result of plasma-beam treatment. It has been found that the degradation is a controlled process and products with a necessary molecular weight can be obtained by appropriately choosing plasma-beam treatment parameters (chemical composition of the plasma gas and treatment time and temperature).

Experimental research on ethanol-chemistry decomposition routes in a microwave plasma torch for hydrogen production

The study of ethanol decomposition process to produce hydrogen using an argon microwave plasma sustained by a Torche à Injection Axiale sur Guide d’Ondes opened to the atmosphere is presented. Different species in the discharge as well as by-products were detected depending on the amounts of both argon and ethanol flows used to sustain the discharge, which were related to the relative influence of air from the atmosphere surrounding the discharge. Furthermore, plasma gas temperature value was found to have a noticeable influence on ethanol decomposition chemistry; giving place to two different ethanol decomposition routes: (i) for higher temperatures (>4500K), ethanol decomposition produced H2, CO and carbon powder, whereas, (ii) at lower gas temperature (<4500K), ethanol was mainly decomposed forming H2, H2O and CO with CO2. These results indicate that the complete ethanol decomposition by means of a microwave plasma sustained with high gas temperatures results in the production of hydrogen through a clean and simple process.

Comparative Studies of Double Dielectric Barrier Discharge and Microwave Argon Plasma Jets at Atmospheric Pressure for Biomedical Applications

Two low-temperature plasma jets using argon carrier gas at atmospheric pressure have been experimentally characterized using optical emission diagnostics. The first one is a double dielectric barrier discharge (DBD) plasma jet generated by a pulsed power supply (9 kV, 9.69 kHz, duty cycle: 1%) and the second one is a microwave (MW) induced plasma jet (2.45 GHz, 40 W ). The argon gas (4.5 purity) flowing through the quartz tube used to launch the plasma in open air is kept at 1 L/min for both plasma devices. Some thermodynamic parameters such as rotation ( $T_{\rm rot}$ ) and excitation ( $T_{\rm exc}$ ) temperatures have been determined as well as some plasma active species such as electron density, ultraviolet C (UVC) irradiance, and atomic oxygen concentrations. Most of these plasma parameters are spatially resolved along the plasma jet axis using the spectra of atomic lines (Ar and O) in the visible range and molecular bands (N2 and OH) in the UV range. At the tube outlet, the electron density and atomic oxygen concentration are one decade higher in the case of the dielectric barrier discharges (DBDs) plasma jet while $T_{\rm rot}$ is higher in the case of the MW plasma jet. These differences are mainly due to the way of plasma generation. Indeed, the guided-ionization waves generated by the DBD setup cause higher nonequilibrium phenomena since the difference between $T_{\rm rot}$ and $T_{\rm exc}$ is shown to be much larger in the DBD case. Furthermore, at the tube outlet, it is shown that UVC irradiance produced by the MW plasma jet is about twice as large as that of the DBD plasma jet. However, at 1.7 cm away from the tube outlet, the differences between the two plasma setups on temperatures and active species production become less significant. For instance, the plasma gas temperature measured with a thermocouple becomes the same (320 K) showing the ability of both plasma setups to be used in biomedical applications without inducing a significant thermal effect.

Optical emission diagnostics of plasmas in chemical vapor deposition of single-crystal diamond

A key aspect of single crystal diamond growth via microwave plasma chemical vapor deposition is in-process control of the local plasma–substrate environment, that is, plasma gas phase concentrations of activated species at the plasma boundary layer near the substrate surface. Emission spectra of the plasma relative to the diamond substrate inside the microwave plasma reactor chamber have been analyzed via optical emission spectroscopy. The spectra of radical species such as CH, C2, and H (Balmer series) important for diamond growth were identified and analyzed. The emission intensities of these electronically excited species were found to be more dependent on operating pressure than on microwave power. Plasma gas temperatures were calculated from measurements of the C2 Swan band (d3Π → a3Π transition) system. The plasma gas temperature ranges from 2800 to 3400 K depending on the spatial location of the plasma ball, microwave power and operating pressure. Addition of Ar into CH4+H2 plasma input gas mixture has little influence on the Hα, Hβ, and Hγ intensities and single-crystal diamond growth rates.

Laser induced fluorescence monitoring of the etching processes with the inward plasma

Laser induced fluorescence (LIF) spectroscopy has been used to monitor the etching processes in a localized plasma etching system. An inward plasma was employed for etching in which etching gas was discharged in the narrow gap between the etched sample and the entrance of an evacuating capillary tube. By observing the LIF spectrum, it was confirmed that the etch product SiF2 exists near the both Si and SiO2 sample surfaces being etched with CF4 inward plasma. The plasma gas temperature was estimated to be ∼400 K from the comparison of the LIF spectrum with the rotational simulation. LIF method was applied to the etching endpoint detection of two kinds of material, thermally-grown SiO2 on Si and spin-coated Polyimide Isoindoro Quinazorindione (PIQ) film on Si. The endpoint was detected from the onset of SiF2 production by the etching of Si substrate in the case of PIQ/Si. The signal intensity of SiF2 from the Si substrate during etching was several times larger than that from the SiO2 layer, and thus, the endpoint of SiO2 etching was detected by the abrupt increase of SiF2 signal. The etch rates of PIQ and SiO2 at the center of the capillary were determined to be 1.09 μm/min and 1.66 μm/min, respectively.

Improvement of the Water Stability of Plasma Polymerized Acrylic Acid/MBA Coatings Deposited by Atmospheric Pressure Air Plasma Jet

A pulsed-arc atmospheric pressure air plasma jet has been used to deposit plasma polymerized acrylic acid/methylene-bis-acrylamide (ppAA/MBA) organic thin films. Optical emission spectroscopy has been performed to investigate the reactivity of the plasma and the dissociation of the precursor as a function of the pulse frequency and distance from the nozzle. An estimation of the OH rotational temperature, which is an indicator of the plasma gas temperature, has also been performed. By heating the substrate during deposition, it was possible to improve to a great extent the stability to water of the coatings. Stable ppAA/MBA films have been obtained with an air plasma over a large range of pulsed frequencies (from 15 to 25 kHz) when the substrate was heated to 200 °C. The composition of these coatings was investigated by FTIR and different amide/acid ratios were obtained, showing the possibility to grow stable films with different functional groups by adjusting the deposition parameters.

Spectroscopic measurement of plasma gas temperature of the atmospheric-pressure microwave induced nitrogen plasma torch

Atmospheric-pressure microwave induced N2 plasma is diagnosed by optical emission spectroscopy with respect to the plasma gas temperature. The spectroscopic measurement of plasma gas temperature is discussed with respect to the spectral line broadening of Ar I and the various emission rotational–vibrational band systems of N2(B-A), N2(C-B) and It is found that the Boltzmann plot of the selective spectral lines from at 391.4 nm is preferable to others with an accuracy better than 5% for an atmospheric-pressure plasma of high gas temperature. On the basis of the thermal balance equation, the dependences of the plasma gas temperature on the absorbed power, the gas flow rate, and the gas composition are investigated experimentally with photographs recording the plasma morphology.

Portable microwave air plasma device for wound healing

A portable microwave air plasma has been developed for safe and effective wound healing. The device is operated by a fixed microwave power and two different air gas flows (main and cooling air flow). It was found that the speeds of the two air flows determine the stability of the plasma jet and gas temperature and thereby regulate the concentrations of the individual reactive species. Two different regimes, i.e. the NO abundant (0.1 slm main air flow) and ozone abundant regimes (4 slm main air flow), were identified as suitable for wound healing without thermal damage and toxicity. These regimes show similar plasma characteristics (e.g. less than 40 °C at the treatment point, less than 4 ppm of NO2) except for different NO and ozone amounts. Both regimes show more than twice as fast wound healing speed compared with the untreated case without any histological damages. Faster healing speed with intrinsic ozone safety make the NO abundant regime the best operation regime for wound healing. Finally, the stability of the developed device was demonstrated by a one-hour continuous operation test with a 24 V battery.

Gas temperature in transient CO2 plasma measured by Raman scattering

Rotational Raman scattering on the vibrational ground state of CO2 was performed to determine the gas temperature in narrow-gap dielectric barrier discharges (DBDs). The Raman spectrometer was equipped with a straightforward spectral filtering to mask ca. 30 cm−1 (0.85 nm) centered around the excitation wavelength of 532 nm. Linearisation of the observed transitions (J = 18–42) was applied to retrieve gas temperatures in discharge gaps of 1 mm. The DBD was operated in pure CO2 at atmospheric pressure and non-negligible gas heating of about 160 K was observed at 33 W injected power. Based on a simplified energy balance the gas temperature measurements were extrapolated to a broad range of injected plasma power values (0–60 W).

Synthesis of Copper Particles by Non‐thermal Atmospheric Pressure Plasma Jet

The present study reveals the synthesis of metallic particles at atmospheric pressure using a radiofrequency low‐temperature argon plasma jet. Copper bulk material of the powered electrode acted as solid precursor in the process and the metallic particles were obtained directly in gaseous environment. The particles were collected onto Si (100)‐oriented substrates downstream of the atmospheric plasma jet and were ex situ characterized via optical microscopy, scanning electron microscopy, X‐ray diffraction, and energy‐dispersive X‐ray spectroscopy. We obtained copper particles, reddish brown in color, either of nano‐ or micro‐metric sizes. Additionally, the plasma species and gas temperature were determined by OES. In conclusion, it was demonstrated that conversion of bulk metals into particles is possible at atmospheric pressure using a radiofrequency plasma jet and the development of several applications is recommended.

Ferrite Loaded DBD Plasma Device

An atmospheric pressure plasma jet device with dielectric barrier discharge was built using low cost 5C22 thyratron valve and ferrite transformer. The ferrite transformer increases the intensity about four times the primary pulse and lengthens the high voltage pulse, keeping the rise time of the thyratron pulse. Spectrometer measurement shows excited nitrogen molecular emissions of second positive system. The most intense nitrogen molecular line, 357.69 nm, was chosen to monitor the time dependence of the discharge. Synthetic temperature, using 380.49 nm line of N2 emission and SpecAir simulation, shows plasma gas temperature of 300 K. To corroborate this low temperature, the plasma jet is applied to human tongue with no harm or bad physical feeling.

Effect of reactor surface modification on the neutral gas temperature in a transformer-coupled toroidal plasma

Transformer-coupled toroidal plasma (TCTP) has found applications in versatile fields as a high-power-density plasma source. However, most research on TCTP has focused on plasma states in the TCTP, without any change in reactor structures. Therefore, in this paper, we present a study on the effects of inner-surface modification of a TCTP reactor on plasma conditions. Using two types of reactors with different inner surfaces, the silicon-wafer etch rate by fluorine atoms from dissociated NF3 gas molecules is compared. Then a computer simulation, which derives various plasma parameters, is carried out. As a result, the TCTP reactor with a grooved inner surface shows a higher etch rate than the reactor with a normal inner surface. The computer simulation suggests the reason for this etch rate difference is that the reactor with the grooved inner surface structure has a higher neutral gas temperature than the reactor with the normal inner surface so that more pyrolytic dissociation, resulting in a higher fluorine atom density, is achieved. Our results may be useful for those fields that require a higher neutral temperature or a higher degree of pyrolysis.

Qualitative gas temperature distribution in positive DC glow corona using spectral image processing in atmospheric air

An experimental method of determining a qualitative two-dimensional image of the gas temperature in stationary atmospheric nonthermal plasma by spectral image processing was presented. In the experiment, a steady-state glow corona discharge was generated by applying a positive DC voltage to a rod-plane electrode in synthetic air. The changes in the gas temperature distribution due to the amplitude of applied voltage and the ambient gas pressure were investigated. Spectral images of a positive DC glow corona were taken using a gated ICCD camera with ultranarrow band-pass filters, corresponding to the head and tail of a N2 second positive system band (0–2). The qualitative gas temperature was obtained from the emission intensity ratio between the head and tail of the N2 second positive system band (0–2). From the results, we confirmed that the gas temperature and its distribution of a positive DC glow corona increased with increasing applied voltage. In particular, just before the sparkover voltage, a distinctly high temperature region was formed in the positive DC glow at the tip of the rod electrode. In addition, the gas temperature decreased and its distribution spread diffusely with decreasing ambient gas pressure.

Experimental and numerical investigation of time evolution of discharge current and optical emission in helium–nitrogen cryoplasmas

Cryoplasmas represent a class of non-equilibrium plasmas whose gas temperature can be controlled below room temperature. However, so far, the influence of the plasma gas temperature on the plasma chemical reactions has not yet been examined in detail. Here we investigated the time-dependent reaction dynamics related to optical emission in helium–nitrogen cryoplasmas. We acquired voltage and discharge current waveforms, optical emission spectra, and observed a temporal change of the emission intensity in helium–nitrogen cryoplasmas at two experimental conditions (temperatures of temperature detector: 5 K and plasma gas temperature: 28 K (condition A), 40 K and 54 K (condition B)). Two time-dependent phenomena were observed: the first was a longer duration of the discharge current compared to that of helium emission at both conditions A and B, and the second was nitrogen ion emission delayed by about 8 µs with respect to the emissions of atomic helium and helium dimers at 40 K. The experimental observations could be reproduced qualitatively by a global reaction model, which took into account the effect of the plasma gas temperature on the reaction rate constants and the diffusion coefficients. The simulations suggested that the reactions related to metastable helium atom were the key reactions, and that the long lifetimes of metastable helium atoms at cryogenic gas temperatures are crucial for the appearance of the time-dependent phenomena. These results imply that the plasma gas temperature is one of the key parameters in non-equilibrium plasma chemistry.

Ozone-Free Portable Microwave Atmospheric Air Plasma Jet

A 1.29-GHz microwave excited atmospheric pressure ambient air plasma jet has been developed as a portable plasma device. A 10-mm stable air plasma jet was generated with a pin-to-hole structure coaxial resonator. Ozone problem was also solved by high temperature of the formed air plasma. Appropriate ambient air flow was supplied to reduce the plasma gas temperature up to 36 °C at treating point. The ozone-free nonthermal portable air plasma system is expected to be useful in biomedical area for its components investigated by optical emission analysis.