Jo Mar 20, 2026
It is very important to theoretically analyse and numerically simulate the ground stability of welded structures, which are of recent worldwide interest.
Packing density and confining pressure have a great effect on the mechanical behavior of sand. Therefore, several kinds of models have been proposed and each of them has their own features.
Fabric anisotropy variable and density function also have a great effect on the mechanical property of anisotropic sand.
Jong Yong Kwang, a researcher at the Faculty of Material Science and Technology, based on the anisotropic critical state theory (ACST), developed a modified anisotropic hypoplastic model by incorporating the relation between fabric anisotropy variable and density function into the nonlinear part of the constitutive model.
He validated the applicability of the improved model by comparing it with the existing model and experimental data.
The results showed that the modified model can well predict the critical state response of anisotropic sand.
You can find more information in his paper “An Anisotropic Critical State Hypoplastic Model Considering the Relation Between Fabric Anisotropy Variable and Density Function” in “Mechanics of Solids” (SCI).
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Jo Mar 19, 2026
Developing an effective, cheap and safe hydrogen storage system is one of the key areas for efficient operation of the hydrogen-based economy.
This area has witnessed many successes by new engineering solutions. However, in order to make rapid technological progress, it is necessary to develop novel materials that can outperform the currently used ones.
Perovskite-type compounds for designing and discovering new materials with target functions can be used for luminescence, photocatalytics, photovoltaics and H2 storage applications.
Jo Son Il, a section head at the Faculty of Material Science and Technology, provided atomic insights into materials properties of double perovskite-type hydride LiNaMg2H6 for H2 storage application.
The results showed that LiNaMg2H6 hydride can be a potential H2 storage material because of its high H2 storage capacity, mechanical and dynamical stabilities and suitable H2 desorption temperature.
If further information is needed, please refer to his paper “Atomic insights into the material properties of double-perovskite-type hydride LiNaMg2H6 for H2 storage applications” in “RSC Advances” (SCI).
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Jo Mar 18, 2026
Transparent conducting oxide (TCO) films have been widely used as transparent electrodes in the optoelectronic devices such as flat panel displays and thin-film solar cells. Among them, Al-doped ZnO (AZO) films are being studied most due to their rich resources of Al and good electrical and optical properties.
The sputtering ambient has an influence on the microstructure, composition and electrical and optical properties of ZnO based films deposited by sputtering.
Some studies showed that adding appropriate amount of H2 into sputtering ambient leads to enhancement of the electrical properties of films. This encouraged many attempts to improve the properties of doped ZnO films by adding H2. However, there is little literature that dealt with the effects of H2 content on the properties of doped ZnO films deposited at low temperature and at high temperature.
Ri Kang Hyon, a section head at the Faculty of Material Science and Technology, compared the influence of H2 addition to sputtering ambient on the microstructural and electrical properties of AZO films deposited by r.f. magnetron sputtering at low temperature (100 ℃) and high temperature (400 ℃).
The results showed that for the AZO films prepared at comparatively low temperature around 100 ℃, small addition of H2 to sputtering ambient was favorable for enhancing the electrical properties of films, but for those at high temperature around 400℃, any addition of H2 was unfavourable at all.
For more information, please refer to his paper “Influence of hydrogen addition to sputtering ambient on the properties of AZO films deposited by sputtering” in “Physica Scripta” (SCI).
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Jo Mar 17, 2026
Selective laser melting (SLM) is one of the most popular advanced manufacturing techniques. SLM is an additive manufacturing (AM) technique that enables production of complicated metal products with high precision and flexibility and acceptable surface finish. It uses a high-intensity laser beam as the energy source to selectively melt metallic powder, which is dictated by 3D CAD data.
SLM enables production of critical parts which are impossible by various traditional metal forming techniques such as casting, forging, extrusion and metal cutting. Unlike the traditional manufacturing techniques, it manufactures 3D objects by gradually adding metal powder layer by layer according to the CAD model. With no need for any dies or tools, it may help to shorten design and production cycles and save time and costs for production.
SLM process parameters affect the multiple quality attributes of SLM-built parts. Thus, it is important to develop a new optimization methodology of SLM process parameters for improving the multiple quality attributes of SLM-built parts. It is a multi-objective optimization (MOO) problem. The multiple quality attributes are converted into a single overall quality index (OQI) using multi-attribute decision-making (MCDM) method, and the MOO problem is converted into a single objective optimization (SOO) one. The optimization results may differ according to the applied MCDM method.
In order to solve this problem, Yang Ji Yon, a post-graduate student of the Faculty of Material Science and Technology, proposed a reasonable process optimization methodology for improving multiple quality attributes of SLM-built parts using integrated OQI (I-OQI) combined with multiple OQIs obtained from multiple MADM methods.
She applied the proposed methodology to optimizing the process parameters such as laser power (LP), scan speed (SS) and overlap rate (OR) for improving five quality attributes of SLM-built AlSi10Mg alloy such as tensile strength, hardness, relative density, volumetric energy density and build rate.
The optimal values of the SLM process parameters obtained from Taguchi and grid search optimization methods were LP 320 W, SS 900 mm/s and OR 0.25.
The proposed methodology could be actively applied to the SLM process optimization of not only Al alloys but also various metal/alloys.
For further details, you can refer to her paper “Process Optimization for Improving Multiple Quality Attributes of AlSi10Mg Alloys Manufactured by Selective Laser Melting Based on Integrated Overall Quality Index” in “Russian Journal of Non-Ferrous Metals” (SCI).
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Jo Mar 16, 2026
Pyrochlore, which contains some rare metals such as tantalum and niobium and many yttrium group rare earths such as erbium and ytterbium, is of very high commercial value. Therefore, it is very important to efficiently recover valuable metals from pyrochlore.
To date, tantalum-niobium ores such as pyrochlore have been treated by using various methods including alkali digestion, acid leaching and chlorination. At present, NaOH or KOH melting digestion method is not applied to the industry due to its low digestion rate, high energy consumption, high reagent consumption and dangerous operations. The consumption of alkali in the pressure leaching is lower than that in the melting digestion, but it is also not applied to the industry due to its operation difficulties. Concentrates are digested at 120-200℃ with concentrated sulfuric acid in the sulfuric acid leaching, which has some drawbacks such as low digestion rate, complex process and high reagent consumption. In the hydrofluoric acid leaching, concentrates are leached at 90-100℃ with 60% HF. This method is now widely used in the industrial processes due to its high tantalum leaching rate (>85%) and easy production of high-purity tantalum. However, the wastes of about 10-15 tons containing fluorine are produced when 1 ton of concentrates is treated, which leads to serious environmental pollution. What is more, the tantalum leaching rate decreases below 85% when low-grade niobium-tantalum concentrates are treated, so this method causes wastage of resources.
Recently, the KOH sub-molten salt (SMS) leaching has been applied to treating ilmenite, vanadium slag, chromite ore and fergusonite, bringing successful results. This technology has several advantages including low environmental pollution, low reagent consumption, mild degradation conditions and high recovery of valuable metals.
Considering all the preceding studies, Kang Chung Su, a section head at the Institute of Analysis, investigated a new decomposition method of pyrochlore concentrate into high KOH solution in order to effectively recover tantalum and niobium from pyrochlore concentrates while reducing environmental pollution at the same time.
The results showed that when the pyrochlore concentrate with a particle size of less than 75㎛ is added to 80% KOH solution in a mass ratio of KOH to concentrate 3:1, and decomposed at 300℃ for 2h at the stirring rate of 80r/min, 95% decomposition rate of pyrochlore concentrate is guaranteed.
You can find more information in his paper “Study on the Environmental Friendly Decomposition Method of Pyrochlore Concentrate in High KOH Solution” in “Proceedings of KUTIC-2025”.
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Jo Mar 15, 2026
The gain and phase information are the important characteristic quantities of frequency domain for stability analysis and control design.
Many researchers have used LMI as an important tool for stability analysis and control design. Although LMI has a limitation that the feasibility is not guaranteed in some cases, it has been widely used in various control problems because it does not require specific assumptions.
Pak Ji Min, president of Kim Chaek University of Technology, presented a solution to the multivariable version of new Ψ-control and H∞/Ψ-mixed control problems with the phase design criterion that enables solving of some control design problems which cannot be achieved by the H∞-control theory.
First, he derived a new phase condition involving linear matrix inequality (LMI) for multi-input multi-output (MIMO) system. He then proved that the phase condition includes the positive real one for a given system and is guaranteed by the bounded real condition for the corresponding transformed system.
Second, he developed new LMI-based solutions to multivariable Ψ-control for both state feedback and dynamic output feedback. He performed H∞/Ψ-mixed control design by combining H∞-control and Ψ-control.
Finally, he illustrated through design examples the significance of phase criterion in the control design, and the effectiveness of the proposed solutions.
For more information, you can refer to his paper “LMI-Based Solution to Multivariable Ψ-Control and H∞/Ψ-Mixed Control Problems” in “Proceedings of KUTIC-2025”.
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