Jo Jul 12, 2023
A research team led by Ho Kuk Chol, a researcher at the Nano Physics Engineering Institute, has made some achievements in their research into determination of catalyst synthesis conditions and cell operation parameters for preparation of ozonized water with dissolved ozone concentration of above 10 ppm, by using nanocomposite catalysts.
Electrode material for producing ozone by electrolyzing water is supposed to suppress oxygen generation by increasing oxygen overpotential and be stable for strong polarization in electrolytes. To date, many anode materials have been developed, including Pt, PbO2, SnO2, boron doped diamond (BDD). These catalysts have advantages and disadvantages in terms of ozone generation efficiency, service life and cost, among which ozone generation efficiency and low cost are considered to be the top priority in the case of sterilizing water used for preventive disinfection.
PbO2 is a catalyst material of significant importance in the technology of ozone generation by water electrolysis. Not only is it inexpensive and can provide high current density, but also it has the characteristics of higher current efficiency under the same electrolysis conditions than Pt.
They prepared a nanocomposite anode catalyst with high ozone generation efficiency by using PbO2 and analyzed its properties before determining the effect of factors on ozone production efficiency.
The nanocomposite catalysts for water electrolyzed ozone generation prove some economic effectiveness.
Although the lifetime is 1/3 of that of precious metal series catalysts, the total cost can be reduced by more than 80%, with only 5% of manufacturing cost.
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Jo Jul 11, 2023
A research team led by Kim Yong Chol, a researcher at the Faculty of Chemical Engineering, has established a method for preparing nano-cuprous oxide by mechanochemical method.
Mechanochemical method, an effective one for obtaining a desired product by simply ball milling reactants in solid phase with mechanical energy required for chemical reactions, has been widely applied recently.
Mechanochemical method is convenient to run and environmentally friendly. In addition, as mechanochemical actions, which increase the driving force of a reaction and the reaction speed, it enables chemical reactions that are impossible or difficult to perform at room temperature.
Therefore, mechanochemical reactions have some characteristics different from ordinary chemical reactions, and reaction mechanisms and thermodynamic and kinetic characteristics are also significantly different from ordinary thermochemical reactions.
Taking into account the factors influencing the preparation of copper oxide from copper sulfate, glucose and sodium hydroxide, they prepared nano cuprous oxide by mechanochemical method.
To prepare nano-cuprous oxide, copper sulphate was chosen as a precursor, glucose as a reductant, and sodium dodecyl sulphate (SDS) as a dispersant for the experiment.
First, required amount of copper sulphate and glucose were pulverized, respectively, and mixed uniformly. Then, pulverized sodium hydroxide and SDS were added to the mixture, respectively, and then ground in a ball mill.
As the milling time increased, the mixture turned from pale blue to orange, and the reaction continued for 50 minutes.
The milled product was taken out, dissolved in distilled water and left to separate the layers. After filtering and washing several times with distilled water and ethanol, they finally obtained nano-cuprous oxide powder by drying it at 60℃ for 4 hours.
The characteristics of the nano-cuprous oxide prepared in the experiments were analyzed by XRD and SEM.
Nano-cuprous oxide prepared in this way can be utilized as a disinfectant at fruit farms, as a photocatalyst in chemical industry and as a colourant in ceramic industry.
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Jo Jul 7, 2023
Hyon Song Chol, a section head at the Faculty of Electrical Engineering, has developed an 800A electrolytic power unit where polarity can be reversed.
Polarity reversion technology can prevent resistance from getting larger and speed of electrolysis from getting slower, due to the silver oxide film formed on the anode during gold refining.
A periodic negative bath voltage makes a silver oxide film separate from the anode. As a result, the fineness of gold and the speed of electrolysis increase with less power consumed.
The polarity reversible electrolytic power unit consists of a full-wave rectifier, a high frequency transformer and a bridge drive unit, a rectifier and filter, and a polarity reversing unit.
The bridge drive unit of the high frequency transformer drives it at 20kHz using phase shift and a soft switching mode.
The voltage at the secondary side of high frequency transformer is then full-wave rectified and filtered, becoming two DC power sources with separated ground.
From these two DC power sources, a negative and a positive voltage are alternatively output periodically by changing the channel with two thyristors at the polarity reversing unit. The polarity reversing unit is constructed in the way of minimizing voltage drop on the current routine, as well as befitting the feature of the thyrister that costs less per unit current but is free from self-closing.
Compared with previous control rectifiers, the voltage distortiong rate is decreased by 5%, the cost by 60% and the weight by 30%.
This device can be used not only as an electrolytic power source unit for non-ferrous metal refining but also as a plating power source unit.
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Jo Jun 29, 2023
Most of the existing routing protocols designed for EH-WSNs (energy harvesting wireless sensor network) are competition-based so they use multiple criteria for CH selection.
To provide balanced energy utilization, factors such as residual energy, distance to BS, adjacency degree, energy harvesting rate were considered and in some protocols even link statistics were included because they help us use a better link to reduce the link loss and ensure the reliability of data transmission.
Especially, in data transmission phase, a transmission power adjustment scheme was introduced to use harvested energy more efficiently. However, in overall operation stages including CH selection, next-hop CH selection and joining CMs to CH, multiple criteria that reflect the property of each node were not used. This resulted in unbalanced utilization of harvested energy.
Also, transmission power adjustment for lengthening the transmission distance was applied only when the rechargeable battery is nearly charged, so it left the possibility to further increase the utilization of the harvested energy.
Especially, energy consumed for sensing was ignored in designing routing protocols under the consideration that it is much less than that consumed for transmission and reception.
To solve the problems above, Ri Man Gun, an institute head at the Faculty of Communications, has proposed a novel improved equal hierarchical cluster-based routing protocol to enhance balanced utilization of the harvested energy as well as to ensure the reliability of communication and the network connectivity.
You can find more information about this in his paper “An Improved Equal Hierarchical Cluster-based Routing Protocol for EH-WSNs to Enhance Balanced Utilization of Harvested Energy” in “IEEE Access” (SCI).
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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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