Jo Aug 15, 2025
With the recent increase in gold production, low-grade, fine-grained gold ores difficult to cyanide and refractory gold ores containing harmful impurities such as sulfur, arsenic, copper, etc. have become the major resources for gold production.
In order to effectively extract gold from the refractory gold ore, oxidative pretreatment must be conducted prior to leaching to oxidize the sulfide bearing gold particles and convert their physical and chemical properties.
There are several pretreatment methods, each with their own advantages and disadvantages. Hydrothermal oxidation pretreatment of refractory gold ores is an effective one, which has been widely used in recent years, due to its high rate of desulfurization, little environmental pollution and high reaction rate.
Sin Hyok, a researcher at the Faculty of Chemical Engineering, has investigated the thermodynamic process of nitric acid oxidation and the factors affecting gold extraction when pyrite-and-arsenopyrite-based gold concentrates are pretreated by mechanochemical activation and nitric acid oxidation.
He has found the following.
The factors affecting gold extraction are nitric acid concentration, mechanical activation time and liquid-solid ratio. The decomposition of pyrite and arsenopyrite in nitric acid medium proceeds from above 1mol/L of nitric acid concentration at room temperature, and the mechanical activation starts decomposition from above 0.5mol/L.
After pretreatment using mechanical activation and nitric acid oxidation, the cyanidation leaching rate for gold concentrates is over 87%.
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Jo Aug 14, 2025
Semiconducting BaTiO3 ceramics are widely used in electronic information, automatic control, biological technology, energy management and traffic control as an important control component. The barium titanate (BaTiO3) shows high intrinsic resistivity of more than 1010Ω·cm when prepared in the oxidizing atmosphere. Therefore, the chemically unmodified BaTiO3, because of its large energy gap, is an electrical insulator. However, when polycrystalline BaTiO3 ceramics are doped with higher valence cations such as Y3+, La3+, Nb5+ or Ta5+, they show semiconducting properties and positive temperature coefficient of resistance (PTCR) effect.
SiO2 and Mn additions assist homogenization of the microstructure during sintering, improving the performance of PTCR under transient loads. In terms of electrical properties, the variation of permittivity with temperature is significantly affected by SiO2 additions: with increasing SiO2, the permittivity increases below Tc.
SiO2 has long been added to BaTiO3 as a sintering aid, but it has not been reported to significantly affect the electrical properties of PTCR thermistors.
Kong Myong Il, a researcher at the Semiconductor Institute, has investigated the effects of SiO2 addition on PTCR characteristics of Y-doped BaTiO3 ceramics prepared by solid-state reaction method.
He has found through the experiments that the optimum SiO2 content was 2mol.
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Jo Aug 13, 2025
At present, most injection molding designers depend on their old experiences in mold design. Due to the diversity and complexity of plastic workpieces and the limited experience of designers, it is difficult to precisely design good-quality products at low cost and in a short period.
Computer Aided Engineering (CAE) analysis techniques are useful for the manufacturing and design of injection molds. The operational tests of injection molds by CAE techniques makes it possible to predict the quality status of plastic products in the forming process of injection molding dies before injection molding. The simulation and analysis using Moldflow instead of operational tests of injection molds at the time of injection mold design help predict the potential defects of injection molds to modify and improve their structure.
Choe Tong Ju, a researcher at the Robotics Institute, has applied CAE simulation analysis to the injection molding of a container into a Hermetia illucens box, and proposed an improved design scheme of die structure.
First, he simulated the flow of plastic melt in the forming chamber. Then, he predicted the best gate position, packing pressure, temperature change, air bubble and weld line position by using the Moldflow software.
Applying the Moldflow to die design helps reduce the cost and the cycle of new product updating by predicting the defects that may occur during the injection process.
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Jo Aug 12, 2025
Generally, the film produced by the chemical film process is not as corrosion-resistant as that produced by the anodizing process, and that is why the chemical film process can only be used for the surface treatment of aircraft skins and non-structural parts.
Unlike the chemical film process, the anodizing process can produce a dense and thick porous oxide layer with excellent corrosion resistance performance. For a thicker and denser oxide layer on the aluminum sheet surface, an aluminum sheet should be immersed in a treatment tank with suitable electrolyte and a direct current or an alternating current should be applied to it. The porous oxide layer provides a large wetting area for adhering, thus enhancing the bonding strength of the aluminum sheet.
Chromic anodizing, sulfuric anodizing, hard anodizing and hot etching are the most commonly used surface treatments of aluminum sheets.
Kim Nam Il, a researcher at the Faculty of Materials Science and Technology, has found the most suitable surface treatment by studying the effect of the four different surface treatments on AlMgSi aluminum sheets when they are bonded with an epoxy-based film adhesive.
He performed four different surface treatments on aluminum sheets that were then bonded with an epoxy-based film adhesive in an autoclave to achieve good adhesion. He examined the microstructure of the porous oxide layer on the aluminum sheet surface and its effect on the bonding performance.
The analysis of the failure modes of the bonded surfaces, the peeling strength and the microstructure of the porous oxide layer showed that chromic anodizing of aluminum sheets have the best bonding performance, whereas sulfuric anodizing and hard anodizing exhibit the worst bonding performance.
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Jo Aug 8, 2025
Spraying is a surface treatment technique whereby the heat source such as an arc or gas flame melts the spraying material and the compressed gas injects it to form a coating on the metal surface. Unlike surface alloying, the coating component is never or rarely diluted by the base metal because it melts none or very little of the base material.
In order to coat mechanical components with mechanical abrasions or casting defects on their surface, the self-propagating high-temperature synthesis method (SHS) is incorporated into the oxygen-acetylene flame spaying. Compared to plasma spraying, oxygen-acetylene flame spraying is cheap, but it is not available for materials with high melting points due to its low flame speed and flame temperature. However, combining the oxygen-acetylene flame spraying with the SHS method is the solution.
Therefore, there have been many studies to spray Al-Fe2O3 materials with good internal friction performance, low cost and high melting points by combining the oxygen-acetylene frame spraying and the SHS method. However, they dealt only with the spraying process and the structures and properties of coating layers in the system, but not reactive thermodynamic analyses.
The desired reaction during spraying and the formation of the structure can be found by reaction thermodynamic analysis. Hence, Jegal Tok Song, a researcher at the Faculty of Materials Science and Technology, has formed an Al2O3-Fe composite coating layer with Fe2O3 and Al powder, cheap belongings to the SHS reaction system, and performed a reactive thermodynamic analysis and a simulation of a spraying process.
First, he verified the possibility of reaction by calculating the adiabatic temperature of the system and the Gibbs free energy of theoretically possible reactions. Then, he performed a differential thermal analysis to determine the temperature for reactions. Finally, he determined the optimum spraying conditions by using Fluent.
The results of his study can also be applied to other reaction systems that involve SHS methods for spraying.
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Jo Aug 5, 2025
In the initial IMO Strategy for reducing greenhouse gas (GHG) emissions from ships, the level of ambition for CII of international shipping was quantified by CO2 emissions per transport work, the average of overall international shipping.
This is a severe rule for ships with only short voyage because the greater the navigation distance is, the lower the CO2 emissions per unit transport work are. In addition, short voyage ships might be evaluated as poor in the CII assessment because of the small transport workday, although measures have been taken to improve energy efficiency. Consequently, all ships will refuse short-term navigation, resulting in a conversion to land transport in some areas. This will lead to an increase in CO2 emissions.
Ri Hyok, a researcher at the Faculty of Shipbuilding and Ocean Engineering, has proposed a relatively fair CII calculation method by introducing a correction factor for an ordinary freight vessel, taking short-voyage and long-voyage into account.
He confirmed the accuracy of correction factors with operational data of ships of less than 35 000 DWT.
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