Jo Sep 19, 2025
Carburization is a technological process for increasing the service life of steel by enhancing its abrasion resistance. However, carburization has low productivity because it takes a long time, and the increase in the carburizing temperature of low carbon steel to reduce carburization time causes coarsening of the prior austenite grains, which results in the decrease in the mechanical properties.
Kim Myong Gwon, a researcher at the Faculty of Materials Science and Technology, has simulated the phase constitutions of low alloy steel 18CrMn and Ti-and-Nb-microalloyed steel 18CrMnTiNb, and analyzed their microstructures and mechanical properties when they were carburized at high temperature.
The steel 18CrMnTiNb, which is microalloyed with 0.06% Ti and 0.06% Nb, has fine grain size after being carburized at 1 000℃. Its prior austenite grain size is less than 25μm. The experimental results show that high-temperature carburization of Ti-and-Nb microalloyed low carbon steels can significantly reduce the carburizing time and provide sufficient mechanical properties.
...
Jo Sep 18, 2025
Graphene, like graphite, is a two-dimensional material of hexagonal structure of carbon. With excellent properties such as high electrical conductivity, thermal conductivity and permeability, it has been widely applied in advanced science and technology fields including graphene composites, electronic materials and energy storage materials.
Several oxidation-reduction methods that are commercially available worldwide are suitable for mass production of graphene, but due to the nature of the processing procedure, many functional groups exist in the prepared graphene, resulting in crystalline defects. In addition, the use of a large amount of strong oxidizing agents causes environmental pollution and the effects of the prepared graphene or graphene oxide on the human body must be considered.
The method of directly obtaining graphene from graphite using shockwave in isopropanol has a disadvantage of low yield, but it is environmentally friendly and nontoxic, so it has a great research value.
Ju Yong Chol, a section head at the Institute of Nano Science and Technology, has prepared few-layer graphene by suspending graphite in isopropanol and applying shockwave generated during pulsed discharge to it, and investigated the effects of charging voltage, capacitor and number of discharges on the number of layers and yield of graphene.
The effects of charging voltage and capacitor on the number of layers of graphene are almost similar. The number of discharges plays an important role in the yield of graphene.
He has analyzed various properties of the graphene prepared using Optics microscope, X-ray diffraction and Raman spectroscopy, and confirmed the presence of 3-6 layer graphene. The yield of graphene is 8%.
...
Jo Sep 17, 2025
With the rapid development of plasma technology, plasma activated water has recently been introduced to agricultural sectors with the potential to increase the germination, growth and grain yield of crops.
Plasma discharge devices to activate water are currently divided into two types. One is to contact various chemical active species produced after plasma discharge in the gas phase with liquid to form secondary active species in it. This is achieved by plasma injection or natural diffusion of plasma activated species such as surface dielectric barrier discharge. The other one is the direct contact of liquid with plasma discharge, and the water is placed in the discharge space. This is achieved by direct plasma discharge between several electrodes, such as a needle electrode or a plate electrode, and water surfaces.
An Song Il, a researcher at the Institute of Nano Science and Technology, has performed water treatment by plasma flow which he formed by high-frequency high-pressure discharge and contacted with water, and compared the production of active species according to two discharge modes (discharge mode using dielectric barrier discharge and discharge mode using a spark discharge between two needle electrodes and water surfaces).
The experimental results show that the plasma treatment mode by dielectric barrier discharge was higher in the production of active species when compared with plasma activated water treated by spark discharge. Therefore, he has concluded that the discharge method using dielectric barrier discharge is superior for mass production of plasma activated water for agricultural applications.
...
Jo Sep 16, 2025
In order to actively develop marine resources for sustainable economic development, it is necessary to identify the types, distribution locations and reserves of seabed mineral resources. All seabed work is impossible without seabed sample exploration, whether it is a study of seabed geological structure or seabed resource exploration.
Ri Jong Chol, a researcher at the Faculty of Shipbuilding and Ocean Engineering, has designed a gravity corer with a spring release mechanism for re-identification of a seabed phosphorite distribution area, and determined the critical velocity before the free fall of the corer designed for sample seabed phosphorites at the depths of 1 000-2 000m.
He has found that the range of critical velocity increases with the increase in the mass of the corer and the decrease in the stiffness of the spring, and that it decreases with the length of a lever arm.
...
Jo Sep 15, 2025
Calculation of riser for steel casting is more important than that for other alloy castings because of the high shrinkage and pouring temperature of cast steels, which leads to severe shrinkage defects.
Among the different calculation methods, the cubic equation method can be used to calculate the shape and dimensions of riser in parametric forms, but it is not widely used due to the large computational amount.
Numerical simulations of the solidification process of cast are more and more used in the design of casting process because of the economy of time and effort as well as the increased accuracy. Many researchers have studied the process of the flow and solidification processes of castings using ProCAST. Most of them, however, found the optimum values by constructing initial design schemes and repeating simulations and modifications. Also, the inclusion of excess mass in the riser is unavoidable, which reduces casting yield.
Hence, it is necessary to establish a methodology to determine the optimum size of the riser while saving the time for simulations.
Ri Hak Song, a researcher at the Faculty of Materials Science and Technology, has set the hydro-powered Pelton turbine blade casting as the main research project, and optimized the riser by combining the numerical simulation analysis by ProCAST with the cubic equation method.
He performed a calculation of the riser by the cubic method and a numerical simulation by ProCAST, a simulation tool for casting processes, to identify the most suitable riser.
The results of the study show that the yield of riser calculated by the cubic method does not differ significantly with the change in the shape of riser, but the elliptical shape is the optimum shape of the riser, with the ratio of height to width of 1.3 and the yield of riser of 67.5%.
...
Jo Sep 14, 2025
Ozone water is made by dissolving into water the gaseous ozone generated during the discharge of oxygen or air or the electrolysis of water.
There are several methods for ozone water production from generated ozone gas, such as porous, bubble tower, U-tube, spray tower, Venturi tube, etc. Among them, venturi-based ozone mixers are widely used, due to their excellent features such as cost, performance, installation area, power consumption, etc.
One of the important ways to increase the concentration of ozone water in the venturi ozone mixer is to increase the amount of ozone gas inhalation into the gas intake. Previous studies only considered the pressure change or velocity change inside the venturi, but not much work has been done on the inhalation volume at the intake.
Rim Chol Bom, a researcher at the Institute of Nano Science and Technology, has determined the optimum geometry of a venturi tube for ozone water production through computational fluid dynamics (CFD) simulations.
The numerical results are inlet diameter of 40mm, throat diameter of 12mm, converging angle of 27° and gas inlet diameter of 7mm, with inhalation rate of 0.100 6g/s.
...