O. H. Chin

Observation of the partial reheating of the metallic vapor during the wire explosion process for nanoparticle synthesis

In this paper, an experimental study using time resolved imaging was reported to study the expansion of the vapor as well as subsequent formation of the arc plasma during the synthesis of Cu nanoparticles by wire explosion process to understand the influences of arc plasma formation on the characteristics of the produced nanoparticles by means of partial reheating of the vapor. Arc plasma is known to form after a delay or immediately depending on the ambience and pressure when the supplied energy is sufficient to sustain the plasma. Observations of two expanding concentric cylinders one inside another by time resolved imaging in the case of delayed formation of arc plasma suggest that the vapor of the wire material is expanding in front of the expansion of the arc plasma. Due to the expansion of the vapor in front of the arc plasma, some of the wire material may not be reheated by arc plasma as opposed to the case of immediate formation of arc plasma, where the vapor is expected to be reheated completely....

A Compact Low Voltage Flash X-Ray Tube

In this paper we describe the construction of a compact, low voltage flash X-ray tube. The device is powered by a small 25 kV, 3300 pF capacitor. Its design is of the vacuum spark configuration with a hollow cathode. The discharge is triggered by a low energy spark behind the hollow cathode; and the triggering spark is also powered by the main capacitor discharge. A 12 kΩ ballast resistor is connected to this auxiliary spark circuit to limit its current. The flash X-ray tube has been operated in air at pressures ranging from 10-1 to 10-4 mbar. At a charging voltage of 25 kV, the flash X-ray tube is able to produce X-ray pulses of several kilowatts in power.

Synthesis of silver nanoparticles prepared in aqueous solutions using helium dc microplasma jet

Silver nanoparticles (AgNPs) were synthesized in aqueous solutions by reduction of silver nitrate (AgNO3) assisted by a helium dc microplasma jet at atmospheric pressure without additional chemical reducing agents. Surfactant-free AgNPs were obtained at low initial AgNO3 precursor concentrations ≤0.5 mM. A surface plasmon resonance peak at approximately 400 nm confirmed the presence of AgNPs. At higher concentrations, sucrose was used to prevent agglomeration and cap the growth of nanoparticles. The effects of the molar ratio of sucrose/AgNO3 on the size distribution and morphologies of AgNPs were investigated. The average sizes of AgNPs synthesized at molar ratios of 20, 50, and 60% were 11.2 ± 0.4, 10.0 ± 0.2, and 6.2 ± 0.1 nm, respectively.

The effects of neutral gas heating on H mode transition and maintenance currents in a 13.56 MHz planar coil inductively coupled plasma reactor

The H mode transition and maintenance currents in a 13.56 MHz laboratory 6 turn planar coil inductively coupled plasma (ICP) reactor are simulated for low pressure argon discharge range of 0.02-0.3 mbar with neutral gas heating and at ambient temperature. An experimentally fitted 3D power evolution plot for 0.02 mbar argon pressure is also shown to visualize the effects of hysteresis in the system. Comparisons between simulation and experimental measurements show good agreement in the pressure range of 0.02-0.3 mbar for transition currents and 0.02-0.1 mbar for maintenance currents only when neutral gas heating is considered. This suggests that neutral gas heating plays a non-negligible role in determining the mode transition points of a rf ICP system.

Effect of neutral gas heating on the wave magnetic fields of a low pressure 13.56 MHz planar coil inductively coupled argon discharge

The axial and radial magnetic field profiles in a 13.56 MHz (radio frequency) laboratory 6 turn planar coil inductively coupled plasma reactor are simulated with the consideration of the effect of neutral gas heating. Spatially resolved electron densities, electron temperatures, and neutral gas temperatures were obtained for simulation using empirically fitted electron density and electron temperature and heuristically determined neutral gas temperature. Comparison between simulated results and measured fields indicates that neutral gas heating plays an important role in determining the skin depth of the magnetic fields.

Investigating the characteristics of a coplanar-coaxial atmospheric pressure dielectric barrier discharge jet in argon

Non-thermal atmospheric pressure plasma jet can easily be generated via a coplanar-coaxial dielectric (quartz tube) barrier discharge configuration driven by AC high voltage source at 11 kHz frequency in flowing argon gas. The plasma jet was characterized by its physical dimension, electrical and optical emission properties. It was found that smaller diameter of the quartz tube produced jets of shorter length. To generate a jet at maximum length for larger tube diameters, higher gas flow rate was required. Increasing the width of the active electrode also produced plasma jets of longer length. Current spikes superposed on the sinusoidal current waveforms were observed when the active electrode of shorter length was used. These spikes diminished when the width of the active electrode was increased to 15 mm. When the active and ground electrodes were inter-changed in position, no plasma jet was formed externally but upstreaming of the jet was observed. No discharge was ignited when the ground electrode was ...

Characteristics Of A Dielectric Barrier Discharge In Atmospheric Air

Parallel plate dielectric barrier discharges consisting of two electrodes with glass (er = 7.5) and alumina (er = 9.0) as the dielectric barrier were constructed. The system is powered by a variable 20 kV high voltage supply which is capable of delivering unipolar voltage pulses at frequency of 0.1–2.5 kHz and sinusoidal voltages at 6.5 kHz and above. At atmospheric pressure, the discharges exhibit either diffuse or filamentary appearance depending on parameters which include the series capacitance established by the electrodes with the dielectric barrier and varying air gap, dielectric material, and frequency of the supply voltages. This DBD system is built for the study of bacterial sterilization.

Simulations of V-I characteristics in a plasma focus fun

The voltage and current characteristics in a plasma focus gun are simulated to yield the current efficiency and the rundown velocity of the current sheath. Since the discharge circuit is strongly influenced by the rundown dynamics of the current sheath, the simple snowplow model, which is modified to include the time-varying current and mass efficiencies, us used. The computer simulations are carried out for two separate experiments using deuterium and argon gas. A steady state of constant rundown velocity and saturated sheath current for both gases is correlated to the maximum holding voltage of the glass insulator. As much as 27% of the total discharge current for the deuterium gas and 33% for argon gas stay behind as leakage currents around the glass insulator when the radial compression phase begins. >

Atmospheric pressure dielectric barrier discharges for sterilization and surface treatment

Atmospheric pressure non-thermal dielectric barrier discharges can be generated in different configurations for different applications. For sterilization, a parallel-plate electrode configuration with glass dielectric that discharges in air was used. Gram-negative bacteria (Escherichia coli and Salmonella enteritidis) and Gram-positive bacteria (Bacillus cereus) were successfully inactivated using sinusoidal high voltage of ∼15 kVp-p at 8.5 kHz. In the surface treatment, a hemisphere and disc electrode arrangement that allowed a plasma jet to be extruded under controlled nitrogen gas flow (at 9.2 kHz, 20 kVp-p) was applied to enhance the wettability of PET (Mylar) film.

Study of non-thermal plasma jet with dielectric barrier configuration in nitrogen and argon

Dielectric barrier discharge (DBD) is advantageous in generating non-thermal plasma at atmospheric pressure, as it avoids transition to thermal arc and dispenses with costly vacuum system. It has found useful applications in treating heat-sensitive materials such as plastics and living tissue. In this work, the discharge formed between the Pyrex glass layer and the ground electrode is extruded through a nozzle to form the non-thermal plasma jet. The DBD characteristics were investigated in terms of charge transferred and mean power dissipated per cycle when operated in nitrogen and argon at various flow rates and applied voltages. These characteristics were then correlated to the dimension of the plasma jet. The mean power dissipated in the DBD was below 7 W giving an efficiency of 17 %. The length of the plasma jet was greatly limited to below 1 cm due to the configuration of the DBD system and nozzle.