Jo Mar 17, 2025
With the recent increase in gold production, the manageable gold ore resources for cyanidation have been gradually depleted, and low-grade, fine-grained gold ores difficult to cyanide and refractory gold ores containing harmful impurities such as sulphur, arsenic and copper have become the main raw material for gold production. Generally, as the ultrafine gold particles are wrapped in pyrite and arsenopyrite in fine grained or disseminated form, gold particles are not exposed even if the ore is finely grinded, which results in low leaching rate for sulphur- and arsenic-rich refractory gold ores. Also, since arsenide reacts with cyanide during the leaching process and consumes the leaching agent and oxygen, it prevents gold leaching.
In order to extract gold from refractory gold ores effectively, oxidation pretreatment must be conducted prior to leaching to oxidize the sulfide-bearing gold particles and convert their physical and chemical properties.
Preoxidation of pyrite and arsenopyrite, especially to compare the oxidation mechanism and the oxidation-reduction potential of sulphur and arsenic and illustrate the effect of desulfidation and arsenic removal on the gold leaching ratio is significant for the pretreatment of the refractory gold ores containing pyrite and arsenopyrite in large quantities.
Kim Chang Sok, a researcher at the Science Engineering Institute, has investigated the thermodynamic features of preoxidation of pyrite and arsenopyrite, the main minerals of refractory gold ores, and the effect of pressure oxidation, one of the peroxidation methods, on chlorination leaching.
From the E-pH diagram of the pyriticarsenopyrite-H2O system, he has concluded that arsenopyrite under acidic conditions is more prone to wet oxidation than pyrite, and that the preoxidation process of pyrite-arsenopyrite-type gold ore can be considered with a focus on the pyrite.
For more information, please refer to his paper “Thermodynamic Behavior of Pyrite and Arsenopyrite in Preoxidation for Chlorination Leaching of Refractory Gold Concentrate” in “Journal of Chemistry” (SCI).
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Jo Mar 16, 2025
At present, the industry is developing rapidly, which results in an increased emission of toxic gases. Therefore, it is of great importance to develop inexpensive and high-performance sensors for real-time monitoring and quantification of these toxic gases in all fields including environmental monitoring, medicine, industrial processing and agriculture. Different types of chemical sensors based on polymers, carbon nanotubes, graphene, zeolites and metal oxide nanomaterials can be used to detect the emission of various toxic gases. Among them, semiconductor gassensors based on metal oxide nanomaterials have attracted a great deal of attention due to their advantages such as excellent fabrication technology, low cost, long lifetime and wide range of target gases. Furthermore, a great interest in them is the integration with complementary metal-oxide semiconductors (CMOS) or microelectromechanical system (MEMS) processes.
Titanium dioxide is an n-type semiconductor with excellent electrical properties, thus finding its wide use in photocatalysis, solar cells and sensors. The surface-to-volume ratio is large for 1D metal oxide semiconductor nanostructures such as nanowires, nanorods, nanobelts and nanofibers. These 1D nanostructures like nanowires and nanorods are widely used for gas sensors. The intrinsic properties of these nanostructures increase the effective surface area of the material by facilitating the interaction with target gas molecules and the diffusion into the material. These nanomaterials are synthesized by hydrothermal method, sol-gel method and electrostatic spinning method to be fabricated by deposition on a substrate.
Some time ago, Pak Jong Sung, a section head at the Faculty of Chemical Engineering, prepared TiO2 nanopaper (long nanowire/nanofiber membranes) similar to the conventional paper in mechanical performance by combining high-temperature hydrothermal nanofiber synthesis and paper preparation, and then characterized its structural properties. This 2D nanomaterial is in disordered arrays of nanowires/nanofibers and of highly porous structure with flexible mechanical strength, and its thickness could be controlled arbitrarily. Thus, this material exhibits intrinsic properties of nanomaterials as sensing materials as well as high chemical, thermal and mechanical stability. However, this material has low selectivity for gas sensing due to the gas sensing properties of semiconductor materials.
To overcome this shortcoming, Ri Son Ho, a student at the same faculty, has prepared a novel gas sensing material with an excellent performance using V2O5-doped TiO2 nanopaper and characterized its SO2 sensing, under the guidance of Pak Jong Sung.
This sensing material exhibited high conversion efficiency of SO2 to SO3 and sensing properties due to its flexible mechanical strength, high porosity, chemical and thermal stability and high catalytic activity of V2O5.
For more information, please refer to his paper “Sulfur dioxide gas sensor based on vanadium oxide doped TiO2 nanopaper” in “Engineering Research Express” (SCI).
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Jo Mar 14, 2025
The permanent magnet synchronous motor (PMSM) is widely used in the robotics and motion control systems due to its compact structure, low noise and high torque to inertia ratio. PMSM is a typical multivariable and nonlinear system with strong coupling and uncertain model parameters. Therefore, traditional linear control methods such as PID control cannot guarantee high control performance for PMSM systems.
Though many advanced nonlinear control methods including adaptive control, nonlinear optimal control, fuzzy logic control and neural network control have been used for PMSM systems, they have their own advantages and shortcomings.
Ri Tae Hyong, a researcher at the Robotics Institute, has proposed a full order terminal sliding mode (FOTSM) controller to solve the speed tracking problem for a PMSM system by combining RBF neural network and FOTSM control scheme.
First, in order to eliminate chattering in conventional sliding mode control (SMC), he developed a continuous FOTSM technique. Then, he designed a FOTSM speed controller based on RBF neural network, in consideration of the presence of external disturbance.
The simulations and PMSM speed control experiments by MATLAB have proved that the proposed method is effective.
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Jo Mar 13, 2025
High-intensity focused ultrasound (HIFU) has been investigated as a noninvasive surgical method for the treatment of tumors located in various tissues including brain, prostate, liver, kidney and breast. When the ultrasonic beams emitted from the transducer is focused into the target tissue, the temperature in the focal region rises above 56℃ in a short time, which results in tissue necrosis without damaging overlying or surrounding tissues.
Recent efforts in HIFU research have been focused on the treatment of uterine fibroids. Uterine fibroid is benign neoplasm that occurs in approximately three out of four menopausal women. The incidence rate of this disease in pregnant women is 25%-30%. Several treatment methods currently exist for uterine fibroids but they have some serious shortages. For instance, hormone therapy is a noninvasive method to treat fibroids but if medication is discontinued, fibroids regrow. These show that HIFU therapy is better than others.
Since the most important requirement in the HIFU therapy is safety, the consequences of the therapy must be predicted before treatments of tumors. Thus, a proper model for predicting the temperature distribution by ultrasound source in a human body is needed.
Kim Sang Jin, a researcher at the Faculty of Physical Engineering, has described and simulated geometrical and mathematical models of the thermal coagulation necrosis region caused by HIFU radiation on the human uterus for different types of transducers and frequencies.
He used two models for the HIFU simulation. In one model, only the linear parts in the Westervelt equation was considered, and in the other one, thermal conduction and viscosity were included. He compared the differences in the temperature distribution for both models, varying the shape of transducer and the frequency.
The results show the shape of transducer and the frequency greatly affect the temperature field in the uterine fibroid.
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Jo Mar 12, 2025
At present, fabrication of micro-scale components and devices is one of the major technologies with considerable potential, and it is of great importance to make manufacturing processes suitable for their medium and large-scale production.
In the last decade, there has been an increasing demand for micro-sized components and their microstructures, which has led to the introduction of micro-injection molding technology to fluid control techniques and medical tools. The most promising process of this technology is micro powder injection molding (μPIM), a product manufacturing technology for producing small size components of complex shapes in large quantities.
However, the μPIM process suffers from several difficulties, unlike the PIM process. In the μPIM process, there is a high demand for powder. For example, the fluidity of raw material depends on the type and size distribution of powder, and the size change after debinding depends on the friction force between particles. In addition, the lubricity of the binder depends on the particle surface conditions, and the debinding rate also depends on the particle morphology, particle size, etc. Raw material powder should be less than 5㎛ in size. The composition of the binder used for mixing raw materials has a great influence on the product's molding and demolding. That is, it needs to have high viscosity. The temperature should be well controlled at the time of debinding of various mixed binders to eliminate cracking during sintering of products and to ensure dimensional accuracy after sintering.
Ri Un Sim, a researcher at the Faculty of Materials Science and Technology, while preparing a 800㎛ micro-gear from 1Cr18Ni9 stainless steel spray powder using μPIM technique, has analyzed the effects of injection temperature, injection pressure and injection speed on the formation of components.
As a result, she has found that injection molding is best at the injection temperature of 130℃, scanning pressure of 70㎫ and scanning rate of 60mm/s.
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Jo Mar 11, 2025
In recent years, it has become a pressing issue in practice to modernize the fish quick-freezing process and increase its productivity in keeping with the huge increase in the catch. The main objective of increasing the amount of quick-freezing production is to automate, streamline and control the quick-freezing process on a high level, along with the use of high-performance quick-freezing equipment. For this purpose, it is necessary to determine appropriate design parameters of a lifting up-down machine (LUDM) for quick-freezing.
So far, there have been many studies on LUDM. At present, machines for transshipping mushroom substrate cases are in use in mushroom farms and LUDMs are used for tiles and roofing tiles in the building materials industry. LUDM for fish quick-freezing has two guide pillars, which involves tipping risk during operation.
Pak Myong Nam, a researcher at the Robotics Institute, has modeled LUDM for fish quick-freezing on SolidWorks, carried out a stability analysis by ADAMS, and determined the design parameters by the quality engineering technique.
Thus, he ensured high accuracy and automation of LUDM, which improved the quality and hygienic safety of fish quick-freezing, saved a lot of labor and realized the automation of the overall fish quick-freezing process.
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