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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Jo Jun 16, 2023
A research team led by Cha Su Song, a researcher at the Nano Physics Engineering Institute, has developed an axial flow microbubble generator capable of adjusting bubble size.
Microbubbles can improve water quality and increase the dissolved oxygen content in water, not only because they are very slow to rise in water and they have high solubility and strong surface adsorption capacity, but also because radicals are produced when they collapse.
The microbubble generation system consists of a water pump, a venturi and an axial flow microbubble generator.
Through the venturi tube installed at the pump inlet flows a mixture of water and air, and when the air–water mixture fluid passes through an axial flow microbubble generator, microbubbles are produced at the generator outlet.
In the microbubble generation system, an air adjusting valve adjusts the flow rate of air sucked into the venturi, and the adjusting valve installed at the outlet of the pump adjusts the bubble size by controlling the internal pressure and flow rate of the mixture inside the generator.
The axial flow microbubble generator consists of a stator and a rotor with shear blades, and the rotor rotates at 8 500rpm to generate microbubbles.
The gap between the stator and the rotor of the generator is 0.3mm.
Through a simulation on the flow rate and bubble generation of a gas–liquid mixing fluid passing through the generator by a computational fluid dynamics (CFD) method, they determined reasonable structural parameters.
The presence of microbubbles produced by this device in water increases bioactivity and metabolic functions of living things and promotes their growth. In addition, they exhibit bactericidal effects and viral inactivation effects depending on the kind of gases that form microbubbles. It can be widely applied in the sectors of public health, agriculture, foodstuff industry, biotechnology and environmental protection,
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Jo Jun 15, 2023
A research team led by O Kyong Ryol, a section head at the Nano Physics Engineering Institute, has developed low-cost ceramic membranes.
Thanks to their unique advantages such as high separation efficiency, excellent thermal and chemical stability and low energy consumption, ceramic membranes have found wide application in gas separation and water purification, and in foodstuff, pharmaceutical and chemical industries.
A ceramic separation membrane is considered as a compound of gradually smaller porous materials, which generally consists of several thin separation layers on a porous support.
In the past years, most ceramic membranes were fabricated as porous ceramic supports with materials such as Al2O3, ZrO2 and SiC or their composites. However, both expensive starting materials and high cost of production processes restricted their extensive applications in industrial fields.
In order to reduce the fabrication cost, they have developed natural kaolin-based ceramic membranes.
Among these porous mineral-based materials, porous mullite ceramics have superior advantages such as good chemical and thermal durability, low expansion coefficient and excellent mechanical properties. These characteristics put them in use as ceramic membrane supports and catalyst supports.
For improvement of the porosity of supports, they are generally prepared by adding pore-forming agents such as corn starch and graphite, but these methods cost a lot and have some defects.
Therefore, as an attempt to solve such problems, they prepared low-cost porous mullite ceramic membrane supports with 2nm pores by extrusion and reaction sintering, with natural mineral kaolin as raw material and Al(OH)3 as a pore-forming agent.
Low-cost porous ceramic membranes are useful filtration components in a number of applications fields, and they will find use in removing contaminants of several micrometers in size down to nanometer range from various fluids.
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Jo Jun 14, 2023
Kang Suk Yong, a researcher at the Faculty of Management of Industrial Economy, has presented a method of assessing rational alternatives of coal separation by DEA.
It is important to stipulate and follow proper assessment procedures for selecting a suitable coal separation plan by DEA in coal mines.
The procedure she has proposed is as follows.
First, a target should be set up and DMU (decision-making unit) be selected.
The target is for proper evaluation of coal separation alternatives. The factors affecting the attainment of the target should be discovered before an analysis of the evaluation object with the target on the centre. Then, the boundaries of DMU and the qualitative and quantitative relationship between them should be determined.
Second, an assessment index system should be determined.
In DEA, evaluation of relative effectiveness for every separation alternative should be made mainly by the input and output assessment indices of each DMU.
Third, a DEA model should be solved.
The solution is for obtaining the assessment results of each DMU.
Finally, results should be analysed.
The solution result of a DEA model makes it possible to attain the optimal DMU to minimize investment and operation cost in coal mines and maximize economic effectiveness at the same time.
Selecting a coal separation alternative by DEA enables us to take measures to produce high quality coal and increase production.
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Jo Jun 13, 2023
Ha Chol Ho, a researcher at the Nano Physics Engineering Institute, has developed PVC-coated cloth and a PVC belt by nano technology.
Polyvinyl chloride (PVC) has been widely used in light industry, chemical industry, building materials industry, etc. because of its low price and good chemical stability.
However, PVC has a defect ― its weak mechanical strength.
The research team has succeeded in manufacturing PVC-coated cloth and a PVC belt by coating textile fabric with PVC paste before being treated with heat.
In order to raise their mechanical strength, they added nano SiO2 and nano CaCO3 to the PVC paste. Then, they chemically modified the surface of the nanoparticles with steric acid to improve the dispersivity of nano SiO2 and nano CaCO3 in the PVC paste.
Finally, they determined the optimal blending ratio by using Multiobject Genetic Algorithms and built its production process.
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Jo Jun 4, 2023
A research team led by Kim Mun Hui, a researcher at the Faculty of Electrical Engineering, has developed a small wind power generation system capable of producing maximum power without a control circuit but a protective reactance coil.
A double-wound permanent magnet generator and a protective reactance coil can reduce harmonic loss and ensure maximum output of a wind turbine by increasing inductance and electromotive force coefficient.
The system consists of a wind turbine, a double-wound permanent magnet generator, a three-phase diode bridge rectifier, an inverter, load, etc.
The rotor of a 2kW wind power generation system is a horizontal axis with three blades and its radius is 1.8m.
The air gap flux density of the double-wound permanent magnet generator is higher than that of conventional ones and the air gap is 0.8mm.
The small power generation system is very effective for power generation of less than 10kW.
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