Jo Jul 24, 2023
Although there are many advantages in SEM measurement methods at ultra-low and low accelerating voltages, it is very important to select a proper accelerating voltage in a wide range from ultra-low accelerating voltage to high one (30kV) according to the purpose of observation of samples.
Studies on imaging of CNTs/polymers have been made within 0.3~5kV of accelerating voltages by FE-SEM with an in-lens detector, but few studies on observation of the surface microstructure of CNTs were conducted by SEM equipped with standard second electron detectors.
Pak Il Man, a section head at the General Assay Office, has performed a theoretical analysis on observation of the microstructure of CNT surface and observed the image of microstructure of CNT surface by Quanta 200 SEM, thus proposing a new method for selecting a proper accelerating voltage.
First, considering the theoretical resolution of Quanta 200 SEM and the size of electron-CNTs interaction range according to acceleration voltage, he made a theoretical study on selection of a proper accelerating voltage.
Second, he performed an observation of SEM images of CNTs at various accelerating voltages.
The effects of energy of the incident electron on the size of the electron-CNTs interaction range and the resolution of SEM were theoretically investigated. As a result, in the case of microstructure observation of CNTs surface by SEM, the most proper accelerating voltage was in the range of 5~10kV.
Through the experiments based on it, he found that the accelerating voltage of 7.5kV enables us to get the sharpest image of the microstructure of CNT surface.
More information is available in his paper “Optimization of the Accelerating Voltage in the Fine Structure Observation of Carbon Nanotube Surface by SEM” in “International Journol of Research and Scientific Innovation” (EI).
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Jo Jul 22, 2023
Hong Won Chol, a researcher at the Faculty of Electrical Engineering, has developed a high-power induction channel furnace (ICF) for melting steel.
Induction channel furnaces (ICF) are widely used for melting, superheating and heat preservation of ferrous and nonferrous metals because of their low power consumption and operation cost. However, thermal stresses in the refractory channel caused by high temperature, premature erosion of the channel due to the flow of molten metal, and failure of the inductor make it difficult to repair them.
He proposed a design of a three-phase channel and an inducer of a new type of ICF for steel melting, and analyzed temperature distribution of the channel by coupling simulations on electromagnetism-heat-fluid, by COMSOL Multiphysics 5.4 and Taguchi method.
An induction channel furnace (ICF) has been widely utilized for melting, refining and heat preservation of metal owing to its advantages such as higher power factor, less power consumption and less stirring of molten metal because the magnetic induction line follows the closed core.
In general, ICF is composed of induction units with iron core, an inductor winding, a channel, and a metal pot. The induction units are assembled verticality to a furnace body, and are separable when the furnace is under repair. The induction units of the proposed ICF are of horizontal type or inclination type, and have no need for separation, so it is easy to repair.
The proposed furnace provides 1 200kW of power, 1.5t/h of output, 1 000V of voltage of inductor (primary winding), 750kW•h/t of power consumption and 4h of cycle of production turns.
This type of furnace, when introduced to the production and refining of steel, cast iron and nonferrous metal, might bring a large profit in operation by saving electrical energy and improving the quality of metals.
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Jo Jul 20, 2023
It is very important to improve rapidity and correctness of analysis.
A powerful chemical imaging analysis system by AI technology has been developed by a research team led by Ri Ok I, a lecturer at the Faculty of Distance Education, and Kim Yong Ok, a section head at the Faculty of Chemical Engineering. They introduced deep learning technology, a branch of mechanical learning that has been accepted as an innovative one in the field of AI technology in recent years, thus making it labor- and cost-effective.
They first developed a method of extracting the main colour from a solution image taken by a camera and converting it into RGB values.
Then, they built a neuron network by deep learning technology. Learning data for the engine should be more than ten thousand sheets but construction of as many experimental data is not easy, so experimental data had to undergo processing for improving learning efficiency.
Finally, they designed it so that the RGB values are put into the engine and output values are processed to show analysis results.
On the basis of this, they developed an analysis system for Android-based smart phones or tablet PCs.
They applied the system to the analysis of Ni plating solution.
The result showed that analysis of plating solutions could be conducted promptly and easily any time with high accuracy without recourse to any kind of chemical reagents and analytical apparatus, and that it can be used by non-professionals too.
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Jo Jul 19, 2023
Today, exhaustion of fossil fuel and serious environmental pollution earnestly require active use of renewable energy resources such as wind, geothermal and solar energies for power generation.
Particularly, geothermal resources with low temperature heat source have been developed extensively for power generation all over the world by using the Organic Rankine Cycle.
A research group led by Ri Hung Nam, a section head at the Faculty of Heat Engineering, has developed a 50kW geothermal power generation system that harnesses hot spring water.
The system consists of an evaporator, a steam turbine, a condenser, a preheater, a hot spring water pump, a working fluid pump and a cooling water pump and so on. NH3 (R717) is used as working fluid.
In the evaporator, the hot spring water from the intake well by the pump produces steam by heating working fluid with low boiling point from the preheater. The high pressure saturated vapor from the evaporator expands through the steam turbine to the pressure of condenser. At the same time, it drives the turbo-generator to generate electricity. In the condenser, the working fluid is condensed with the help of the cooling water.
The condensed working fluid is fed to the preheater by the pump.
In the preheater the working fluid from the condenser is heated to be saturated liquid with an evaporating temperature by the hot spring water from the evaporator. Hot spring water from the preheater is used for heating of a building. And the heated working fluid in the preheater enters into the evaporator and then the above cycle is repeated.
This system has horizontal bundle heat exchangers (evaporator, condenser and preheater) and a single impulse stage steam turbine.
In the evaporator hot spring water flows into the tube and working fluid evaporates outside. In the preheater, working fluid flows into the tube and hot spring water flows out of it.
In the condenser, cooling water flows into the tube and working fluid vapor is condensed outside.
The system saves 120~180t/h of coal a year and it can contribute to the prevention of global warming. It is available in all areas with over 70℃ of heat sources such as hot spring and wasted heat.
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Jo Jul 17, 2023
A research team led by Jang Pok Nam, a section head at the Faculty of Metal Engineering, has established an Nd-Fe alloy production process for rare earth magnet by using rare earth resources in our country.
Because of its great activity and its good properties, rare earth metal is widely used in various fields including the metallurgical and electronic automation industries and the field of its application is being widened more and more.
Especially, Nd-Fe-B system rare earth magnets have the best characteristics of all magnets that have been developed so far, and their application in various industrial fields brings great economic profits.
Neodymium-iron alloy is a main material for production of Nd-Fe-B magnets.
The research team has established a system of producing Nd-Fe by rare earth fluoride-oxide molten salt electrolysis.
Compared to chloride electrolysis process, fluoride-oxide electrolysis process has good adaptability to raw materials and it enables production of various rare earth metals and alloys.
Fluoride-oxide electrolysis, a method by which the composition of electrolytes is not changed and neodymium oxide is periodically supplemented, makes possible continuous production without any limits of electrolysis time.
The Nd-Fe production process consists of electrolyte manufacturing process and electrolytic production process.
In the electrolyte manufacturing process, anhydrous neodymium fluoride is produced from neodymium chloride.
In the electrolytic production process, Nd-Fe alloy is produced in a graphite crucible with a pure iron electrode as a cathode and a carbon electrode as an anode.
Under electrolytic conditions, the current efficiency is 68~69%, the direct yield of neodymium is 92%, and the power consumption is 13.7 kW•h/kg.
The content of neodymium in the neodymium iron alloys produced is very high with more than 85%, and the non-rare earth content is very low, so that the alloy can be used for the production of magnets directly without undergoing a refining process.
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Jo Jul 15, 2023
A research team led by Kim Yong San, a researcher at the Faculty of Electrical Engineering, has developed a small wind power generation system capable of ensuring maximum efficiency in low wind speed regions.
For efficiency improvement, they applied average wind speed determination method based on left truncation Weibull distribution to the design of blades of a wind turbine. As a result, the average wind speed was determined to be 4.4m/s in the region with yearly average of 3m/s and on this basis the efficiency was improved by 13%.
The system consists of a three-blade horizontal axis propeller wind turbine, a three-phase permanent magnet generator, a control device, an inverter, load and so on.
Applying this method to small wind turbines usually used in low wind speed regions, they were able to produce more electrical power from the same amount of wind.
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