Corona Discharge Technique Research Articles

Drop-On-Demand Microdroplet Generation under Charge Injection by Corona Discharge.

In printing, microreactors, and bioassays, the precise control of micrometer-scale droplet generation is essential but challenging, often restricted by the equipment and nozzles used in traditional methods. We introduce a needle-plate electrode corona discharge technique that injects charges into an oil layer, enabling the precise manipulation of droplet polarization and splitting. This method allows for meticulous adjustment of microdroplet formation regarding location, size, and quantity by modulating the discharge voltage, discharge time, and electrode positioning. It enables the immediate initiation and cessation of droplet production, thereby facilitating on-demand droplet generation. Our study on the voltage-dependent droplet stretch coefficient shows that as the voltage increases, the droplets transition from controlled splitting to regular Taylor cone-like ejections, eventually reaching the Rayleigh limit and fully breaking apart. These advancements significantly improve microfluidic droplet manipulation, offering considerable benefits for applications in targeted drug delivery, rapid disease diagnostics, and precise environmental monitoring.

Gold nanospheres assembly via corona discharge technique for flexible SERS substrate.

Noble metal nanoparticles (NMNPs) assembly substrates with strongly enhanced local electromagnetic fields provide new possibilities for surface-enhanced Raman spectroscopy (SERS) sensing. Although the external-electric-field-based self-assembly (EEFSA) strategy for decreasing NMNP gap in liquid phase is relatively developed, it is rarely described in solid phase. Here, by combining corona discharge technique (CDT) as a simple EEFSA approach on flexible substrate surface modification, a flexible SERS substrate medicated with gold nanospheres (AuNSs) is produced. Because of the CDT's peculiar discharge event, makes AuNSs aggregation simply achieved. The modified flexible SERS substrate is sensitive to the detection limit of ∼10-5 mM for Rhodamine 6G (R6G), with a maximum enhancement factor of 2.79×106. Furthermore, finite-difference time-domain (FDTD) simulation confirms the SERS enhancement impact of AuNSs-based substrate. This study not only provides a low-cost, simple-to-process, high-yield, high sensitivity, and activity flexible SERS substrate, but also suggests a more practical and adaptable NMNPs self-assembly approach.

An Investigation of Factors Affecting Measurement Accuracy of Nanoparticles Real-time Sensor using Corona Discharge integrated with Quartz Crystal Microbalance

A nanoparticles real-time sensor in the present study was designed using corona discharge integrated with quartz crystal microbalance (QCM) or Nano-QCM detector. We investigated the following factors affecting the measurement accuracy of the detector; needle to plate distance, flow rate, and number of particles on QCM. DC high voltage power supply of 7 kV was used to maintain the positive corona voltages difference in the charger. The mass sensitivity of 10 MHz AT-cut QCMs coated by plate rigid gold film were investigated. The monodisperse aerosol particles smaller than 300 nm were initially used for the testing of the system. They were charged with negative corona voltages and then deposited on the surface of QCM electrode. Sauerbrey equation was used to describe the frequency-mass relationship at the QCM surface. Results show that the above factors significantly affect the accuracy of the detector measurement. The particles can be collected on a QCM electrode using the partial breakdown high voltage (reach to breakdown points) in terms of needle-to-plate corona discharge. The optimal needle-to-plate distance is 6 mm with maximum mass change (frequency shift) on QCM electrode of 0.607μg/min. The QCM collection efficiency of nanoparticles on the QCM electrode surface using corona discharge technique can be as high as 95% of total particles. Collection efficiency of PM0.1 is under investigation.

Electrostatic Effects of Corona Discharge on the Spectrum and Density Evolution of Water Droplets in Air

As one of the emerging application areas of the corona discharge technique, rain enhancement induced by atmospheric air ionization has made a great breakthrough. Although natural rainfall modified by artificial ionization was successfully observed via the statistical data of field experiments, deficient efforts have been devoted to the research on the near-field effect of corona discharge on the evolution of water droplets around the discharge device. In this article, we studied the electrostatic effects of corona discharge on the spectrum and density evolution of water droplets in a 96-m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> cloud chamber. An interesting phenomenon was found that two different electrostatic effects appeared when various high voltages were applied on the corona electrode. In detail, the growth of droplets larger than 10 μm was detected once the applied high voltage exceeds the critical value (e.g. -80 kV in our discharge device), and this is attributed to the electrostatic induction effect. By contrast, a narrow droplet size spectrum and reduced density caused by the strong electrostatic precipitation effect were shown below this critical voltage. To figure out the mechanisms underlying these phenomena, the charging status of water droplets with various sizes, forces of charged droplets under various electric field strength, and collision kernels between droplets, are analyzed through theoretical calculations. Results show that the electric field plays a dominant role in the charging process of droplets and the acceleration of collision-coalescence between charged and neutral droplets, which results in the different electrostatic effects on the evolution of droplets. This article may provide some enlightenment to fog elimination in industrial application and cloud-seeding in atmospheric water resources comprehensive utilization.

Effect of electrostatic precipitator on exhaust emissions in biodiesel fuelled CI engine.

The exhaust emissions from the compression ignition engines are harmful to both human beings and the environment. After-treatment devices placed in the exhaust are designed to reduce these emissions. These devices have significant conversion efficiency but have various drawbacks such as the cost and availability of the precious catalyst for catalytic converters. In this work, an emission reduction setup was developed that can reduce NO, HC, CO and smoke simultaneously. The emission reduction setup is based on the concept of an electrostatic precipitator (ESP) and plasma generation by corona discharge technique. Both diesel and waste cooking oil biodiesel (WCO) were separately used for the test. The results show that HC emissions at full load with ESP system reduced from 0.71 to 0.27g/kWh for diesel and for WCO it reduced from 0.81 to 0.31g/kWh. Similarly, the CO emissions reduced from 1.50 to 0.6g/kWh for diesel and from 1.95 to 0.92g/kWh for WCO. The smoke emission and NO emission were also reduced by 30.86 and 29.3% for diesel and WCO and 17 and 18% for diesel and WCO, respectively. However, the carbon dioxide emissions were found to increase as the HC and CO generated were also converted to CO2. The study shows that the emission reduction setup can effectively reduce the emissions without any effect on the engine performance.

Effects of FeSO4 and H2O2 on earthed atomizing corona discharge technique for the styrene-butadiene rubber wastewater treatment

Effects of FeSO4 and H2O2 on earthed atomizing corona discharge technique for the styrene-butadiene rubber wastewater treatment

Numerical simulation and experiments on mono-polar negative corona discharge applied in nanocomposites

The corona discharge techniques, which are employed to orient dipoles and built up charges inside functional polymers, can develop important commercial applications of electroactive polymers (EAPs) and electrets for energy storage devices, air filters, electroacoustic and electromechanical transducers. We propose hereby an elective hybrid approach to the point-plane corona modeling in order to obtain more accurate electron flow in unipolar corona discharge system. A coupled system of partial differential equations (PDEs) w.r.t. Navier-stokes equations and hydrodynamic drift diffusion equations described the nature of photo-ionization, where the secondary avalanche in the discharge process was demonstrated. The simulation was verified by comparison with Surface Potential (SP) measurement of the nano-composites after corona polarization. Consequently, the spacial electric potential distribution and initial surface potential could be obtained by the means of finite elements method (FEM), which provided a good numerical approach for the experimental data of electrostatic surface potential. In addition, the influence of nano particle on the charge retain ability of the insulating polymers was also investigated, which could be a guideline for designing an effective poling method on the functional polymers applied in electrical energy storage devices sensors, actuators and transducer etc.

Analysis on Magnetoelectric Responses of Porous Polypropylene and Polyvinyl Chloride after High-Voltage Corona Discharge

In order to enhance the electromechanical performance of functional polymers for their application in the fields of robot, sensors, transducer and actuators etc., the high voltage corona discharge equipment has been used in this paper with the aim of injecting a large amount of electrons into the Porous Polypropylene (PP) and Polyvinyl Chloride (PVC). In addition, the performances of magnetoelectric effect of porous PP and PVC between before and after corona discharge have also been discussed for the first time. It is shown that their magnetoelectric current of porous PP and PVC can be increased by the corona discharge technique. We have established the fact that enhanced ME performance could be achieved by using effective corona poling method on porous polymer and not only by adding micro or nanoadditives.

Oxidative coupling of methane in a corona discharge plasma reactor using HY zeolite as a catalyst

Oxidative coupling of methane in the presence of corona discharge plasma has been studied for the production of higher hydrocarbons under the conditions of ambient temperature and atmospheric pressure. The corona discharge was created by applying 3 kV (DC) between a tip and a plate electrode, 1.5 and 2.5 mm apart, in a tubular reactor. The effects of variables such as methane to oxygen ratio, total flow rate, electric current and more importantly, electrode gap distance were investigated. The electrode gap distance affected the electric field strength and subsequent plasma reactions. Five electrodes shaped like needles in the tip plate were applied to create more discharge intensity. At CH4/O2 ratio = 4, total flow rate = 4 mL/min, electric current = 10 mA and electrode gap distance = 1.5 mm, 31.9, 58 and 55 % of C2 yield, C2 selectivity and methane conversion, respectively were achieved. The main products were ethane, ethylene, acetylene, while CO and CO2 were also observed. The corona discharge interaction with HY-zeolite catalyst has led to low temperature methane conversion. Thus, the effect of surface modified zeolite catalyst was also examined. At a CH4/O2 ratio of 4 and total flow rate of 4 mL/min, 59.4, 69.7 and 85.3 %, of C2 yield, C2 selectivity and methane conversion, respectively were achieved. Experimental results revealed that corona discharge techniques, in the presence of HY-zeolite catalyst, has potentials for improving methane conversion, C2 selectivity and C2 yield.

In situ wafer-level polarization of electret films in MEMS acoustic sensor arrays

Polymer electrets, polymers with a quasi-permanent electrostatic polarization, are commonly employed in a macro-scale form factor within transducers such as the electret condenser microphone. In addition, MEMS-based electret transduction has been reported for both acoustic sensors and energy harvesters. In these micro-devices, the polymer film is typically polarized prior to assembly into the device. Common techniques employed in MEMS electret polarization include corona discharge and backlighted thyratron, with wafer-bonding and simple stacked assemblies being employed to perform the actual assembly and integration. In contrast, this paper reports a method for post-release in situ polarization of electret films within a MEMS device. The method utilizes microplasma discharges with self-aligned charging grids integrated within the device to charge fluoropolymer films in a fashion similar to the corona discharge technique. This in situ approach enables the integration of uncharged electret films into MEMS and subsequent post-fabrication charging, simultaneously enabling the formation of buried or encapsulated electrets as well as eliminating the need to restrict fabrication processes that might otherwise discharge pre-charged electret materials. The method is applied to a single-chip array of ultrasonic sensors designed to capture and analyze waveforms from impacts.

In-Situ Wafer-Level Polarization of Electret Films in MEMS Acoustic Sensor Arrays

MEMS-based electret and polymer piezoelectric transduction techniques have been reported for both acoustic sensors and energy harvesters. Common techniques employed in MEMS polymer polarization include corona discharge and backlighted thyratron. This paper reports a method for post-fabrication in-situ polarization of polymer films embedded within the MEMS device itself. The method utilizes microplasma discharges with self-aligned charging grids integrated within the device to charge fluoropolymer films in a fashion similar to the common corona discharge technique. This in-situ approach enables the integration of uncharged polymer films into MEMS and subsequent post-fabrication and post-packaging polarization, simultaneously enabling the formation of buried or encapsulated electrets as well as eliminating the need to restrict fabrication and packaging processes that might otherwise discharge pre-charged materials. CYTOP, a thermoplastic fluoropolymer encapsulant for electronics, is used as a polymer electret in the current process because it can be spin-cast, has a high resistivity, and is easily etched in oxygen plasma. A microscale charging grid structure is then fabricated and suspended a short distance above the polymer film. After fabrication of the charging grid, standard microfabrication steps are performed to build a single-chip array of MEMS capacitive acoustic sensors designed to capture and analyze waveforms from impacts. After completing the entire fabrication and packaging flow, the polarization process is performed. When energized by a high voltage, the sharp metal edges of the charging grid lead to high dielectric fields that ionize the air in the gap and force electric charge onto the polymer surface. Final sensor arrays have been demonstrated and applied in the classification of acoustic stress pulses generated during impacts of various materials.

Progress in unipolar corona discharger designs for airborne particle charging: A literature review

Particle motion induced by electrical forces is the basis for important class of measuring instruments. Charging is important in aerosol size measurement. Unipolar charger is a crucial component in the aerosol particle sizing system by electrical mobility analysis. For an electrical mobility analyzer, the charging is aimed to impose a known net charge distribution on each aerosol size. The charger performance depends on the charging efficiency and stable operation. A well-designed unipolar charger should provide high charging efficiency and stability that can be accurately determined for any given operating conditions. This article presents and discusses progress on the development of existing unipolar aerosol chargers based on corona discharge technique. The operating principles as well as detailed physical characteristics of these chargers, including the corona-wire and corona-needle chargers, are described with extensive list of references.

Surface graft copolymerization of 2‐hydroxyethyl methacrylate onto low‐density polyethylene film through corona discharge in air

AbstractThe corona discharge technique was explored as a means of forming chemically active sites on a low‐density polyethylene (LDPE) film surface. The active species thus prepared at atmospheric pressure in air was exploited to subsequently induce copolymerization of 2‐hydroxyethyl methacrylate (HEMA) onto LDPE film in aqueous solution. The results showed that with the corona discharge voltage, reaction temperature, and inhibitor concentration in the reaction solution the grafting degree increased to a maximum and then decreased. As the corona discharge time, reaction time, and HEMA concentration in the reaction solution increased, the grafting degree increased. With reaction conditions of a 5 vol % HEMA concentration, 50°C copolymerization temperature, and a 2.0‐h reaction time, the degree of grafting of the LDPE film reached a high value of 158.0 μg/cm2 after treatment for 72 s with a 15‐kV voltage at 50 Hz. Some characteristic peaks of the grafted LDPE came into view at 1719 cm−1 on attenuated total reflectance IR spectra (CO in ester groups) and at 531 eV on electron spectroscopy for chemical analysis (ESCA) spectra (O1s). The C1s core level ESCA spectrum of HEMA‐grafted LDPE showed two strong peaks at ∼286.6 eV (CO from hydroxyl groups and ester groups) and ∼289.1 eV (OCO from ester groups), and the C atom ratio in the CO groups and OCO groups was 2:1. The hydrophilicity of the grafted LDPE film was remarkably improved compared to that of the ungrafted LDPE film. © 2001 John Wiley &amp; Sons, Inc. J Appl Polym Sci 81: 2881–2887, 2001

Surface graft copolymerization of acrylic acid onto LDPE film through corona discharge

In this work the corona discharge technique was explored as a means of forming chemically active sites onto the low density polyethylene (LDPE) film surface. The active species thus prepared at atmospheric pressure in air is exploited to induce simultaneously copolymerization of acrylic acid (AA) onto LDPE film in aqueous solution. The results show that with the corona discharge treatment time, treatment voltage and inhibitor concentration in reaction solution, the grafting degree increases, but decreases after passing a maximum. As the reaction time, temperature and AA concentration in reaction solution increase, the grafting degree increases. Under the condition of 20% by volume AA concentration, 70°C copolymerization temperature and 1.5 h reaction time, the grafting degree of LDPE film after treated 72 s reaches a quite high value of 220.55 μg cm −2. Some characteristic peaks of the grafted LDPE come into view at 1574 cm −1 on ATR-IR spectra (>CO in –COONa group on the grafted LDPE film surface neutralized with NaOH) and at 531 eV on ESCA spectra (O 1s), their intensities increase with grafting degree. The hydrophilicity and the peel strength of grafted LDPE film are improved remarkably as compared with that of the ungrafted LDPE film.

Highly Efficient Organic/Inorganic Hybrid Nonlinear Optic Materials via Sol−Gel Process: Synthesis, Optical Properties, and Photobleaching for Channel Waveguides

The thermally stable second-order nonlinear optic (NLO) hybrid materials were successfully prepared by a sol−gel process using dye-attached sol−gel monomers (ormosils) of difunctionalized or trifunctionalized second-order NLO chromophores attached to silicon atoms. The dye-attached sol−gel monomers were synthesized by the coupling reaction of 3-isocyanatopropyltriethoxysilane with the corresponding functionalized NLO chromophores in DMAc. The dye-attached sol−gel monomers were homopolymerized and copolymerized with TEOS by hydrolysis and polycondensation in the presence of a slight excess amount of acidified water (pH 3), yielding the hybrid precusors (or a homogeneous solution). The hybrid precursors were spin-coated on various substrates such as ITO glass and NaCl disk. Hybrid films were further polycondensed by curing at 170 °C for 3 h. The cured hybrid materials existed in monohydroxy (T2, Q3) and nonhydroxy (T3, Q4) states, indicating the formation of a highly cross-linked silicon−oxygen polymeric network. All of the cured organic/SiO2 hybrid films are transparent. The organic/SiO2 hybrid materials were quite stable at elevated temperatures above 250 °C. The hybrid films were poled by corona discharge technique or dc contact electrode. The values of electro-optic coefficient for the organic/SiO2 hybrid materials were in the range of 3.7 to 16 pm/V at the wavelength of 1.3 μm, depending on dye-attached sol−gel monomers and poling conditions. The SG-DANS (1:2:2) film shows excellent temporal stability. The r33 signal remained at 80% of its initial value after heating even at 150 °C for 3 h. Also, the second-order nonlinear optical coefficient d31 of 72 pm/V for the SG-DANS (1:2:0) hybrid film measured by the Maker fringe technique was obtained. The refractive index was decreased after photobleaching. Using the hybrid film, a single-mode channel waveguide was also fabricated by the photobleaching method. The mode pattern confirmed that a channel waveguide was single-mode, and the optical propagation loss was measured to be less than 1 dB/cm.

Oxidation of ammonia in moist air by use of pulse corona discharge technique

The gas-phase decay of NH 3 at different concentrations in moist air by combined corona discharges and UV irradiation in static and flow conditions has been studied. An effective oxidation of NH 3 with conversion near 100% has been obtained. The mechanism of NH 3 oxidation with participation of different intermediates (ions, atoms, radicals) has been considered.

Copolymerization of styrene on to cellulose activated by corona

AbstractThe corona discharge technique was explored as a means of forming chemically active sites on cellulose surfaces. Paper thus treated was brought into contact with the reaction medium, a styrene–methanol mixture.The corona discharge was generated between two flat circular electrodes separated by a quartz disk. Scanning electron microscope analysis and wettability studies indicated that a hydrophobic film coated the cellulosic fibers.The molecular weights of both the homopolymer and the copolymer were characterized by GPC. Two peaks for grafted copolymer were observed, the first having about the same average molecular weight as the homopolymer, and the second having a molecular weight of about ten times the first fraction.A polymerization mechanism is proposed.

Stress Relaxation in SiO2 Films on Silicon by a Negative Point Oxygen Corona Discharge

As integrated circuit fabrication technology moves toward smaller device geometries, low‐temperature (≤900°C) processing has become important. An alternate method for achieving high‐quality stress‐free layers on Si using a negative point oxygen corona discharge technique is discussed. Isotope tracer structures are used to investigate the corona‐induced relaxation mechanism. Some electrical properties of corona‐relaxed oxides are presented. Two‐step oxidation experiments are used to determine oxidant transport properties of corona‐processed films.

Breakdown voltage of silicon chlorine oxides

The breakdown voltage of Si-SiO 2 structures obtained by thermal oxidation of silicon in a dry oxygen atmosphere with the addition of HCl has been investigated after hydrogen plasma treatment. The measurements are carried out by the specially developed corona discharge technique, which gives the possibility of determining the breakdown voltage of Si-SiO 2 structures without a gate electrode. The results show that the breakdown voltage decreases after plasma treatment. The process of decrease is explained by the creation of oxide traps in the SiO 2 after plasma treatment. It is found that the breakdown voltage depends on plasma power.

Electrostatic charge occurrence, significance and measurement

Polymeric materials often have a resistance to earth in excess of 10 6ω. This condition results in the ability to accumulate and store electrostatic charge over significant periods of time. Once an electrostatic charge has been gained (either by tribocharging or corona discharge techniques) it reduces at a rate depending on the resistivity of the material, and on the level of charge remaining on the material. The dependence of charge decay rate on charge magnitude is described by the relaxation equation; however, charge decay values are often quoted (for a fixed time period). Such values can be ambiguous and often lead to erroneous conclusions; a new ‘performance rating’ system is introduced here, giving an accurate and easily interpreted indication of charge decay rate and charge levels involved. Measurements of surface charge are obtained by electrostatic fieldmeters, one of which is linked to a data-logger for automatic data collection for manipulation and presentation of results. This procedure enables accurate assessment of antistatic systems and atmospheric effects (such as relative humidity).