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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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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