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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Jo Jul 13, 2023
A research team led by Kim Kang Su, vice-dean of the Faculty of Shipbuilding and Ocean Engineering, has designed and constructed a multi-purpose ladder-dredger.
Several kinds of multi-purpose dredgers are being used all over the world for river and coast improvement, ecological environment protection and prevention of flood damage.
The dredger they have newly constructed works with several dressing machines and discharging equipment for different purposes ― a excavator bucket, a drum screen, a washer, a concentrator, discharging equipment, anchorage posts and elevators.
When the sands and gravels are dropped down from the bucket, they are separated individually while being washed by the water from a pump. The separated sands are transported into the concentrator and the gravels are conveyed to the ship by the belt conveyor.
The concentrator separates high density ores from the sands by using the jig. The separated sands are moved through the drain into the transfer tank and loaded on the ship by the bucket-type conveyor and the belt conveyor.
When working, the dredger holds its position and posture by 2 fore anchors and 1 aft anchor.
All the equipment is comprehensively controlled in the control room.
The multi-purpose ladder dredger will keep the environment cleaner for river improvement, thus contributing to the prevention of flood damage.
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Jo Jul 12, 2023
A research team led by Ho Kuk Chol, a researcher at the Nano Physics Engineering Institute, has made some achievements in their research into determination of catalyst synthesis conditions and cell operation parameters for preparation of ozonized water with dissolved ozone concentration of above 10 ppm, by using nanocomposite catalysts.
Electrode material for producing ozone by electrolyzing water is supposed to suppress oxygen generation by increasing oxygen overpotential and be stable for strong polarization in electrolytes. To date, many anode materials have been developed, including Pt, PbO2, SnO2, boron doped diamond (BDD). These catalysts have advantages and disadvantages in terms of ozone generation efficiency, service life and cost, among which ozone generation efficiency and low cost are considered to be the top priority in the case of sterilizing water used for preventive disinfection.
PbO2 is a catalyst material of significant importance in the technology of ozone generation by water electrolysis. Not only is it inexpensive and can provide high current density, but also it has the characteristics of higher current efficiency under the same electrolysis conditions than Pt.
They prepared a nanocomposite anode catalyst with high ozone generation efficiency by using PbO2 and analyzed its properties before determining the effect of factors on ozone production efficiency.
The nanocomposite catalysts for water electrolyzed ozone generation prove some economic effectiveness.
Although the lifetime is 1/3 of that of precious metal series catalysts, the total cost can be reduced by more than 80%, with only 5% of manufacturing cost.
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Jo Jul 11, 2023
A research team led by Kim Yong Chol, a researcher at the Faculty of Chemical Engineering, has established a method for preparing nano-cuprous oxide by mechanochemical method.
Mechanochemical method, an effective one for obtaining a desired product by simply ball milling reactants in solid phase with mechanical energy required for chemical reactions, has been widely applied recently.
Mechanochemical method is convenient to run and environmentally friendly. In addition, as mechanochemical actions, which increase the driving force of a reaction and the reaction speed, it enables chemical reactions that are impossible or difficult to perform at room temperature.
Therefore, mechanochemical reactions have some characteristics different from ordinary chemical reactions, and reaction mechanisms and thermodynamic and kinetic characteristics are also significantly different from ordinary thermochemical reactions.
Taking into account the factors influencing the preparation of copper oxide from copper sulfate, glucose and sodium hydroxide, they prepared nano cuprous oxide by mechanochemical method.
To prepare nano-cuprous oxide, copper sulphate was chosen as a precursor, glucose as a reductant, and sodium dodecyl sulphate (SDS) as a dispersant for the experiment.
First, required amount of copper sulphate and glucose were pulverized, respectively, and mixed uniformly. Then, pulverized sodium hydroxide and SDS were added to the mixture, respectively, and then ground in a ball mill.
As the milling time increased, the mixture turned from pale blue to orange, and the reaction continued for 50 minutes.
The milled product was taken out, dissolved in distilled water and left to separate the layers. After filtering and washing several times with distilled water and ethanol, they finally obtained nano-cuprous oxide powder by drying it at 60℃ for 4 hours.
The characteristics of the nano-cuprous oxide prepared in the experiments were analyzed by XRD and SEM.
Nano-cuprous oxide prepared in this way can be utilized as a disinfectant at fruit farms, as a photocatalyst in chemical industry and as a colourant in ceramic industry.
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Jo Jul 7, 2023
Hyon Song Chol, a section head at the Faculty of Electrical Engineering, has developed an 800A electrolytic power unit where polarity can be reversed.
Polarity reversion technology can prevent resistance from getting larger and speed of electrolysis from getting slower, due to the silver oxide film formed on the anode during gold refining.
A periodic negative bath voltage makes a silver oxide film separate from the anode. As a result, the fineness of gold and the speed of electrolysis increase with less power consumed.
The polarity reversible electrolytic power unit consists of a full-wave rectifier, a high frequency transformer and a bridge drive unit, a rectifier and filter, and a polarity reversing unit.
The bridge drive unit of the high frequency transformer drives it at 20kHz using phase shift and a soft switching mode.
The voltage at the secondary side of high frequency transformer is then full-wave rectified and filtered, becoming two DC power sources with separated ground.
From these two DC power sources, a negative and a positive voltage are alternatively output periodically by changing the channel with two thyristors at the polarity reversing unit. The polarity reversing unit is constructed in the way of minimizing voltage drop on the current routine, as well as befitting the feature of the thyrister that costs less per unit current but is free from self-closing.
Compared with previous control rectifiers, the voltage distortiong rate is decreased by 5%, the cost by 60% and the weight by 30%.
This device can be used not only as an electrolytic power source unit for non-ferrous metal refining but also as a plating power source unit.
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