Jo Jun 27, 2023
A research team led by Kim Myong Hui, a researcher at the Nano Physics Engineering Institute, has developed a dielectric barrier discharge (DBD) ozone generator power supply, and analyzed the discharge characteristics of load through a simulation on the ozone generator power supply circuit by MATLAB 7.0 to increase ozone production and improve the efficiency of the ozone generation supply.
The DBD ozone generator is largely composed of an ozone generating tube and an inverter power supply. In order to increase ozone production, it is necessary to improve the efficiency of the power supply by matching the power supply and the ozone generating tube.
The DBD ozone generator power supply consists of a rectifier, a filter, an inverter and a booster.
For matching, they connected the compensation inductor for constructing the resonant circuit in series with the circuit.
Then, they carried out a simulation analysis of a voltage-type load series resonant DBD ozone generator power supply by MATLAB Simulink. The main parameters of the simulated DBD ozone generator power supply are input voltage 220V/50 Hz, power 600W, frequency 4kHz, transformer primary voltage 250V, secondary voltage 3 000V, discharge gap capacitance 1nF and dielectric capacitance 5nF.
The simulation result demonstrates that if a resonant circuit is constructed by series connection of the compensation inductor to the transformer primary or secondary side, the load current and discharge voltage phases are almost identical, i.e., the matching of the power supply and the ozone generating tube can be ensured and the efficiency of the power supply can be raised.
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Jo Jun 26, 2023
Quality index and quality map have been used to evaluate the quality of cast aluminum alloys quantitatively and intuitively.
Quality index and quality map quantitatively evaluate the quality of cast aluminum alloys according to yield strength (YS), ultimate tensile strength (UTS), elongation to fracture (Ef), and strain energy density (W).
There are some quality indices such as Q, QR, QC, and Q0. Quality maps are generated to intuitively evaluate the quality level based on quality indices. These quality indices and quality maps show the quality levels according to the pairs of tensile mechanical properties such as UTS and Ef, or YS and Ef, or YS and W.
By using these quality maps, it is impossible to directly evaluate the quality levels according to the artificial aging heat treatment condition.
Yang Won Chol, a researcher at the Faculty of Materials Science and Technology, has developed multiple quadratic polynomial regression models and quality maps for tensile mechanical properties and quality indices of the cast aluminum alloys according to artificial aging heat treatment conditions.
Then, he has evaluated the performances of the regression models using the mean absolute errors, mean relative errors, and coefficients of determination.
The proposed regression models and quality maps could widely be used to evaluate the quality of the cast aluminum alloys according to the aging heat treatment conditions and determine the rational aging heat treatment condition.
You can find details of this in his paper “Multiple Quadratic Polynomial Regression Models and Quality Maps for Tensile Mechanical Properties and Quality Indices of Cast Aluminum Alloys according to Artificial Aging Heat Treatment Condition” in “Advances in Materials Science and Engineering” (SCI).
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Jo Jun 25, 2023
A research team led by Kim Su Gil, a researcher at the Nano Physics Engineering Institute, has investigated time-dependent deposition of ozone at different depths in bulk grains.
Treatment of grains by ozone gas can remove bacteria, pests and contaminants from bulk grains. In addition, it causes no secondary contamination due to the self-dissolution of ozone after treatment.
Because of good post-treatment results, ozone treatment is considered to be a very effective and eco-friendly method for improving grain quality.
For better understanding of ozone penetration in treatment of bulk grains by ozone gas, they investigated time-dependent deposition of ozone at different flowing velocities and depths in bulk grains.
They proposed a model of deposition in bulk grains by applying a material balance of ozone in a column of stored grains. The deposition model shows flow rate of ozone gas, porosity of bulk grains and pore shape factor.
The deposition model was applied to determine the time-dependent deposition velocities of ozone at different depths from measured values of ozone concentrations in columns of wheat grains. Then, penetration of ozone into columns of wheat grains was evaluated by analysing deposition velocities.
The deposition model makes it possible to estimate the ozone deposition on bulk grains in the treatment of different kinds of stored grains by ozone gas, and to design ozone treatment processes.
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Jo Jun 22, 2023
The electrochemical characteristics of a soluble lead flow battery are key factors for improvement of its cyclic lifetime and efficiency.
Ho Yu Gyong, a researcher at the Nano Physics Engineering Institute, has proposed aqueous solution of Pb(BF4)2 and HBF4 as the electrolytes of a soluble lead flow battery, and observed the kinetic behavior of the electrode by cyclic voltammetry, the cyclic lifetime, quantum efficiency and voltage efficiency of the SLFB with respect to concentration of the electrolyte.
The conductivity exhibits a peak at 1.5mol/L Pb(BF4)2 when [HBF4] is below 1.0mol/L while it decreases with the increase in the concentration of Pb(BF4)2 when [HBF4] is higher than 1.0mol/L.
According to the cyclic voltammetry, the electrode process is fast with a low overvoltage and no additional reactions for the aqueous solution with 1.5mol/L Pb(BF4)2 and 0.25mol/L HBF4.
Overall, for the aqueous solution of 1.5mol/L Pb(BF4)2 and 0.25mol/L HBF4, the battery showed the best performance with the cyclic lifetime 48 times, the average quantum efficiency 88%, the voltage efficiency 70% and the battery efficiency 62%.
These results are promising for fresh parameters of the electrolyte that could play a major role for the improvement of SLFBs.
For more information, please refer to her paper “Study on electrochemical properties of Pb(BF4)2 electrolyte for improvement of cycle lifetime and efficiency in soluble lead flow batteries” in “Journal of Saudi Chemical Society” (SCI).
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Jo Jun 21, 2023
A research team led by Kim Jin Hyok, a researcher at the Nano Physics Engineering Institute, has developed an ozone generating tube of floating net electrode structure by covering a steel tube with nano-composite materials.
Ozone generation technology enables prevention of spread, infection and breeding of all kinds of infective viruses and sterilization of objects, air and water, etc. by ozone with marvelous germicidal power produced by physical devices without recourse to noxious chemical disinfectants.
An ozone generating tube works in a high voltage electric field. At the time of generating ozone, it gets hot and it has strong corrosiveness, so dielectric material for it must satisfy several properties (electric characteristics such as dielectric coefficient, coefficient of dielectric loss and electric strength, corrosion resistance, resistance to thermal shock, abrasion resistance, etc.) simultaneously.
To satisfy these characteristics, they decided to coat a steel tube with nano dielectric material in three layers. First, they newly developed undercoat borosilicate system glass ceramic material that satisfies the adhesive capacity with the steel tube and determined a suitable calcination process. Then, to develop a reasonable interfacial layer for ozone generation, they newly suggested a dielectric coefficient simulation algorithm of nano-composite materials based on a mixed state model and determined the mixing ratio of the materials.
On this basis, they established an appropriate process for production of ozone generating electrodes, produced a large capacity ozone generating tube, and proved the predominant properties.
An ozone generator equipped with these ozone generating tubes is very effective for sterilization of water, air and objects in several fields like foodstuff production and processing, interiors of buildings like hospitals, etc.
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Jo Jun 19, 2023
CdTe material, which has high absorption coefficiency and optimum bandgap as well as stability, has been widely used as an absorber of thin film solar cells.
In general, a pure CdTe thin film contains Cd vacancies of lower concentration, with composition ratio of Te/Cd<1 and low p-type conductivity. However, due to the self-compensation of Cd vacancy, it is difficult to obtain a p-type CdTe semiconductor thin film. In addition, a CdTe polycrystalline thin film with high grain boundary density and large surface area particles has high boundary activity and a large number of defects, therefore resulting in high grain boundary barrier and many recombination centers which lower the photo-generated carrier density to decrease photoelectrical properties. In order to prepare good semiconductor materials, it is necessary to improve the conductivity and structural properties by doping donor or acceptor-like impurity.
Kim Hyon Chol, a researcher at the Faculty of Electronics, has analyzed the dependence of the microstructure and properties of thin films on the Te rich content and heat treatment of CdTe:Te films, to obtain the following results.
As Te rich content increases, diffraction intensity becomes stronger, which gets the highest at Te rich content of 5%, indicating that crystallinity of a film is improved and the defects and stress become less. At high Te rich contents (7, 10%), the grain growth does not change with Te rich content.
The incorporation of impurity Te atoms into a CdTe lattice affects lattice structure and preferential growth of crystal whereas extra Te atoms enter into grain boundaries, which is unable to make Te rich content affect the crystal growth of a thin film.
For the sample annealed in air after CdCl2 treatment, (111) peak has a significant preferential orientation and increase of each peaks indicates grain growth and good crystallinity.
Performance parameters of solar cells increase and then decrease with increase in Te rich content, and maximum efficiency is attained at Te content of 5%.
If further information is needed, please refer to his paper “The effect of Te-doping and heat treatment on the structural properties of CdTe absorber layer for CdS/CdTe solar cell” in “optical materials” (SCI).
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