• Korean Journal of Materials Research
• /
• v.19 no.12
• /
• pp.661-666
• /
• 2009

Froth flotation has been carried out in order to produce roasting-molybdenite concentrate from molybdenite ore in the Shin-yeomi mine. In our study, roasting-molybdenite (Mo 0.43%) from Shin-yeomi mine was recovered by varying the conditions of regrinding time, dosage of collector and alkalinity. Liberation and flotation efficiency more were effective at regrinding time of six minutes than at single grinding. Mo recovery curves increased considerably as dosage of kerosene increased, whereas Mo grade curves decreased gradually. The separation efficiency of molybdenite was effective when the dosage of collector (kerosene) was adjusted to 300 g/t. The molybdenite concentrate was agglomerated in the range of pH 5-7 and its separation efficiency increased to pH 9-10. The concentrate of 49.5% Mo grade ($MoS_2$, 82.6%) with 81.5% recovery from Shin-yeomi molybdenite ores was obtained under conditions of 20% pulp concentration, 300 g/t kerosene 325 g/t frother (AF65), 2.5 kg/t depressant ($Na_2SiO_3$), pH 9-10 and four cleaning times. In the future, a trial run that can separate up to 50% Mo grade from Shin-yeomi molybdenite ores will be performed.

• Journal of the Korean institute of surface engineering
• /
• v.49 no.2
• /
• pp.159-165
• /
• 2016

The hydrogen has been recognized as a clean, nonpolluting and unlimited energy source that can solve fossil fuel depletion and environmental pollution problems at the same time. Water electrolysis has been the most attractive technology in a way to produce hydrogen because it does not emit any pollutants compared to other method such as natural gas steam reforming and coal gasification etc. In order to improve efficiency and durability of the water electrolysis, comprehensive studies for highly active and stable electrocatalysts have been performed. The platinum group metal (PGM; Pt, Ru, Pd, Rh, etc.) electrocatalysts indicated a higher activity and stability compared with other transition metals in harsh condition such as acid solution. It is necessary to develop inexpensive non-noble metal catalysts such as transition metal oxides because the PGM catalysts is expensive materials with insufficient it's reserves. The optimization of operating parameter and the components is also important factor to develop an efficient water electrolysis cell. In this study, we optimized the operating parameter and components such as the type of AEM and density of gas diffusion layer (GDL) and the temperature/concentration of the electrolyte solution for the anion exchange membrane water electrolysis cell (AEMWEC) with the transition metal oxide alloy anode and cathode electrocatalysts. The maximum current density was $345.8mA/cm^2$ with parameter and component optimization.

• Resources Recycling
• /
• v.24 no.3
• /
• pp.11-15
• /
• 2015

In order to develop a technology for the recovery of pure tin from the Sn containing industrial wastes (SIWs), a process consisted of high temperature reduction and electrorefining was investigated. The tin which exists as oxide in SIWs was successfully reduced by two consecutive high temperature treatments and 92.7% of the tin was recovered. The purity of the tin thus obtained was increased to 99.87% by electrorefining. By applying the results obtained in this work, a commercial process can be developed to produce pure tin metals from domestic spent resources, which can reduce the amount of tin imported from abroad.

• Journal of Korea Foundry Society
• /
• v.38 no.3
• /
• pp.60-65
• /
• 2018

In the present study, the characteristics of Mg inverter cases for hybrid cars are investigated. Concerns over the use of lightweight materials to reduce energy use and to mitigate emission problems are inevitable in the twenty-first century. Magnesium is a promising material for the manufacturing of lightweight parts. Several cases for thermal cooling channels have been designed and simulated, and the effects of materials and coatings on the thermal cooling efficiency have been discussed. The effects of the coating thickness on heat extraction in an Mg inverter housing case using the PEO (plasma electrolyte oxidation) coating method were also discussed. In order to produce an inverter case by the diecasting process, the filling sequence and cooling behavior during the diecasting process were simulated. The optimized process conditions from the simulation result were then used in a trial diecasting experiment.

• Korean Journal of Materials Research
• /
• v.29 no.1
• /
• pp.16-22
• /
• 2019

Indirect oxidation using chlorine species oxidizing agents is often effective in wastewater treatment using an electrochemical oxidation process. When chlorine ions are contained in the wastewater, oxidizing agents of various chlorine species are produced during electrolysis. In a ballast water management system, it is also used to treat ballast water by electrolyzing seawater to produce a chlorine species oxidizer. However, ballast water in the brackish zone and some wastewater has a low chlorine ion concentration. Therefore, it is necessary to study the chlorine generation current efficiency at various chlorine concentration conditions. In this study, the chlorine generating current efficiency of a boron-doped diamond(BDD) electrode and insoluble electrodes are compared with various chloride ion concentrations. The results of this study show that the current efficiency of the BDD electrode is better than that of the insoluble electrodes. The chlorine generation current efficiency is better in the order of BDD, MMO(mixed metal oxide), $Ti/RuO_2$, and $Ti/IrO_2$ electrodes. In particular, when the concentration of sodium chloride is 10 g/L or less, the current efficiency of the BDD electrode is excellent.

• The korean journal of orthodontics
• /
• v.21 no.3
• /
• pp.543-560
• /
• 1991

Practitioners are aware of the presence of friction between bracket system and archwire during sliding movement of teeth. Clinically a mesiodistally applied force must exceed the frictional force to produce a tooth movement. The objective of this study were to determine, on a dry condition, changes in magnitude of friction with respect to load, 3rd order inclination (Torque), archwire materials and ligature type. Three wire alloys (Stainless Steel, TMA, NiTi) in two wire sizes (.016, .016x, .022 inch) were examined respect to two bracket system (Straight, Standard), and two ligature type (Metal, Plastic ligature) at three levels of load (100g, 150g, 200g). The results were as follows; 1. Frictional resistance was found to increase with increasing load for S.S., TMA, NiTi. 2. The straight bracket system was exhibited more frictional force than standard bracket system for .016x, .022 S.S. tightly ligated metal ligature. But, torque difference did not increase friction for loose metal ligature & plastic ligature. 3. Regardless of the ligature type, torque and load, stainless steel wire sliding against stainless steel exhibited the lowest friction, and TMA sliding against stainless steel exhibited the highest friction. 4. The loose stainless steel ligature generated lower frictional resistance than plastic ligature in all experimental groups. 5. The following factors affected friction in decreasing order; wire material ligature type, and load.

• Advances in concrete construction
• /
• v.7 no.3
• /
• pp.151-166
• /
• 2019

This paper introduces a new efficient analytical method, based on shear deformations obtained with 2D elasticity theory approach, to perform an explicit closed-form solution for calculation the interfacial shear and normal stresses in plated RC beam. The materials of plate, necessary for the reinforcement of the beam, are in general made with fiber reinforced polymers (Carbon or Glass) or steel. The experimental tests showed that at the ends of the plate, high shear and normal stresses are developed, consequently a debonding phenomenon at this position produce a sudden failure of the soffit plate. The interfacial stresses play a significant role in understanding this premature debonding failure of such repaired structures. In order to efficiently model the calculation of the interfacial stresses we have integrated the effect of shear deformations using the equilibrium equations of the elasticity. The approach of this method includes stress-strain and strain-displacement relationships for the adhesive and adherends. The use of the stresses continuity conditions at interfaces between the adhesive and adherents, results pair of second-order and fourth-order coupled ordinary differential equations. The analytical solution for this coupled differential equations give new explicit closed-form solution including shear deformations effects. This new solution is indented for applications of all plated beam. Finally, numerical results obtained with this method are in agreement of the existing solutions and the experimental results.

• Proceedings of the Korean Society for Emotion and Sensibility Conference
• /
• 2001.05a
• /
• pp.147-155
• /
• 2001

Nasucon lamp and Russian ones, which are coated with some special materials on the glass bulb, gave good clinical results for a cancer therapy. They are experimentally studied with Automatic Bioelectric Response Recorder on the six placements of the electrodes (two feet, two hands and two foreheads). They reduced the current rather than the control (natural) state. However infrared lamp and Chinese God light did not reduced the value current. Hemoglobin in blood. Brown gas, Ti$_3$SiC$_2$ and Nasucon have planar crystallizing $\pi$-bonding bonding layer and covalent bonding one in sequence commonly and thus the alternating magnetic fields are protected. Nasucon lamp and Russian ones utilized electric bulbs in order to generate alternating magnetic fields and to produce absorbing force.

• Transactions of Materials Processing
• /
• v.23 no.8
• /
• pp.475-481
• /
• 2014

Water quenching is one method of cooling after hot forming, which is presently being used for the manufacturing of automobile parts. The formed parts at room temperature are heated and then cooled rapidly in a water bath to produce high strength. The formed parts may undergo excessive thermal distortion during the water quench. In order to predict the distortion during water quenching, a coupled thermo-mechanical simulation is needed. In the current study, the simulation of heating and cooling of boron steel cylinders was performed. The material properties for the simulation were calculated from JMatPro, and the convective heat transfer coefficient was obtained from experimental tests. The results show that the thermal distortion and the residual stresses are well predicted by the coupled simulation.

• 제어로봇시스템학회:학술대회논문집
• /
• 2001.10a
• /
• pp.99.4-99
• /
• 2001

PMAC(Permanent magnet AC) motor drives are widely used in the industrial applications and home appliances because of high torque ratio, high efficiency and precise control performance. In recent years there has been a significant development of PMAC motors of various kinds. Improvements in the properties of permanent magnet materials have increased the viability of related types of motors. However, precise speed and position information is essential for the good control performance. In order to produce correct torque, the rotor flux position information from position sensor has to be identified. In this paper, a low cost position sensor is proposed for improving of starting and low speed performance of PMAC. The proposed position ...