Jo Jul 8, 2025
Manganese is an important alloying element indispensable in the metallurgical industry and it is widely deposited in the form of oxides in nature.
The reduction reaction of manganese oxides in the production of metallic manganese or ferromanganese from these manganese raw materials is of great importance, and there have been many thermodynamic and kinetic studies on it. In particular, several kinetic models describing the carbothermic reduction reaction of MnO have been proposed and experimentally examined.
However, there are some errors in the calculation and experimental results in the models proposed by the previous authors, and no studies have yet applied the fractional order to the kinetic modeling of the reduction reaction of MnO by solid carbon.
Kim Un Dok, a researcher at the Faculty of Metal Engineering, has developed a kinetic model for the reduction process by solid carbon of MnO in high-carbon ferromanganese slags using fractional differential equations (FDE), determined the relationship between fractional order, fractional rate constant and temperature, and verified the accuracy of the fractional order model through the comparison with the results of previous studies.
Comparing the preset values calculated from the FDE and previous models with the experimental values, the root-mean-square errors (RMSE) were 0.005 and 0.029, respectively, and the coefficients of determination were 0.999 and 0.980, respectively, which shows that the proposed model is more accurate.
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Jo Jul 7, 2025
Aluminum and its alloys have light weight, good thermal and electrical properties, excellent mechanical properties and process ability, and low cost, so they are widely used in various fields of the national economy such as the mechanical industry, aerospace, daily necessities industry, electronic industry, building materials industry, etc. Aluminum and its alloys are easily oxidized in the atmosphere because of their strong chemical activity, resulting in a thin oxide film on the surface, which is protective because of its good corrosion resistance in dry air, but it is easily damaged in contaminated atmosphere, water, seawater, soil and various corrosive media, which is not protective. Therefore, surface treatment is carried out to enhance the surface performance of aluminum and its alloy, such as corrosion resistance, wear resistance and decorativeness.
At present, the sealing of anodized aluminum alloy is carried out at high temperature, which leads to high energy consumption and low productivity.
Kim Chang Sok, a researcher at the Science Engineering Institute, has investigated the sealing mechanism of Ni-F system to realize room temperature sealing, one of the ways to reduce energy consumption and shorten the production cycle in the sealing process for surface treatment of aluminum alloy, and investigated the influence of various factors on the room temperature sealing quality to confirm a reasonable room temperature sealing process index.
Through the room temperature sealing experiments of aluminum alloy 6061, he has found that the optimum conditions are Ni2+ concentration of 1.5g/L, F- concentration of 2g/L, sealing temperature of 20~30℃, sealing time of 15~20min and pH of 5.5~6.5.
The surface properties of the samples sealed at room temperature are superior to the surface properties of the existing sealed samples at high temperature. In addition, the sealing temperature can be lowered by over 70℃ and the time for sealing can be shortened by 15 minutes, which leads to the decrease in energy consumption for heating sealing solution and the increase in productivity.
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Jo Jul 6, 2025
Tobacco has been grown in our country since the end of the sixteenth century. At the beginning, it was used for medicines, and it gradually turned into crops for luxury items, which led to further spread in its cultivation.
Around the end of the seventeenth century, tobacco culture was spread to every part of the country, and as a result, some places famous for tobacco culture came into being.
The most famous place of them all was Songchon area of South Phyongan Province.
From long ago, Songchon Tobacco was called “gold thread” as it resembles gold thread when it is cut into thin strips and “Songchon fragrant tobacco” for its fragrance. After that, it finally got its name “Songchon Tobacco” as it is from Songchon.
President
Thanks to the wise guidance of the Workers’ Party of Korea, Songchon Tobacco is still gaining worldwide fame as one of the famous specialties of Korea.
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Jo Jul 4, 2025
Multistage centrifugal pumps are commonly-used pieces of turbomachinery for applications with high head and flow duty requirements. So, the improvement of their technological indexes is greatly significant for saving energy, ensuring production and raising economic benefit.
Since the axial force in high-pressure multistage pumps reaches tens of tons, it is essential to balance hydraulic axial thrust. Even then, an axial bearing is required; and its size depends largely on the prediction accuracy of axial thrust and on the type of the balancing device. Therefore, the size of bearings and the axial thrust balance systems of multistage pumps are frequently determined on the basis of axial force measurements carried out on each particular type and hydraulic pressure of pumps.
In general, balancing devices are used for balancing the axial thrust acting on the rotors of multistage centrifugal pumps. Balancing devices create forces that oppose the axial thrust generated by the impellers. When dimensioned correctly, balancing devices are able to completely balance the axial thrust, so the required pressure automatically builds up in the radial gap due to an axial displacement of the rotor. Therefore, the axial clearance at the device depends on the axial force acting on the rotor, i.e. on the operation point of the pump.
Balancing devices have two gaps: a radial gap and an axial clearance. The mutual coupling of these two gaps allows automatic balancing of the axial force. According to the variation of operation point of a centrifugal pump, the axial thrust changes. The rotor moves left and right in the axial direction to be in a new equilibrium state, when the axial clearance changes with the movement.
If the axial displacement of the rotor is too large, the balancing device may contact with the casing to cause wear. Thus, the rotor vibrates and the stability of operation is destroyed. Therefore, when balancing device is designed, even small axial displacement must yield large changes in the balancing force. In previous studies, this performance was estimated by sensitivity coefficient.
Sensitivity factor represents the variation of balancing force according to the pressure distribution in front and rear shrouds of impeller, but does not represent variation of balancing force when a rotor moves. Therefore, it can be more correct to estimate the automatic balancing ability of a balancing device by the parameter representing the variation of balancing force when a rotor moves a unit length.
Han Pok Nam, an institute head at the Faculty of Mechanical Science and Technology, has decided leakage through radial and axial clearance, pressure difference and balancing force based on the theoretical analysis of the gap flow of a balancing device. Then, he has defined a new concept of stiffness coefficient and analyzed the relationship between stiffness coefficient and geometrical parameters.
Thus, he has found that the stiffness coefficient decreases with too large or too small sensitivity coefficient, and a reasonable sensitivity coefficient should be chosen around 0.5.
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Jo Jul 3, 2025
It is well known that TEA-CO2 laser is a kind of high-power laser with enough pulse peak output, and study on TEA-CO2 laser has been consistently conducted for a long period of time. The design of electrode structure, which emits field electrons in TEA-CO2 laser, is a question of finding an effective method for increasing laser power by raising the emission efficiency of field electrons and their utilization.
In practice, the tips of cold-cathode are made in the shape of a needle or a blade. Such tips emit field electrons at low discharge voltage by raising the amplification degree of electric field. When the electric field strength at the tips is too high, the lifetime of tips will be shortened owing to the cathode sputtering. The field electron generator that contains cold-cathode provides high vacuum of 10-4Pa.
The Marx generator supplies electric power to the generator of field electrons. Here, such geometric parameters as the height and basal width of tips and the size of anode cells are all related to the amplification degree of electric field. The electric field strength at the tips is affected by not only the shape and size of each tip but also their arrangement. When high voltage is applied to the cathode, the existent electric fields in the vicinity of the tips interact with each other, which obviously influences the electric field strength at the tips.
Pak Sin Hyok, a researcher at the Institute of Nano Science and Technology, has designed an electrode structure of cold cathode and grid anode with a high amplification degree of electric field strength at the tip, in consideration of the tip’s parameters, the arrangement of electrode structure, etc.
He designed the tips as a triangle, and simulated the electric field in the discharge region by the COMSOL Multiphysics software while changing the size and array interstice of tips and the dimension of grid anode corresponding to the tips. On this basis, he found out the optimum design parameters of electrode for raising the amplification degree of electric field strength at a tip to the maximum.
The simulation result shows that the optimum interstice of tips that provides the maximum amplification degree of electric field was 8mm, and the amplification degree of electric field strength was 1.2.
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Jo Jul 1, 2025
July is the hottest month of the year.
The seasonal divisions in July include Soso and Taeso.
Soso means the gradual beginning of hot weather. It falls on early June by the lunar calendar that falls on 6th-8th of July by the solar calendar.
Taeso means the spell of the hottest weather. It falls on late June by the lunar calendar that falls on 22nd-23rd of July by the solar calendar.
Around Soso and Taeso, all kinds of cereals and fruits grow exceptionally fast. Therefore, frequent weeding and good care of the crops at this time of year guarantees bumper harvest.
July has early dog days and mid dog days. They are two of the three dog days, the hottest period of the year.
Our people have cooked several kinds of dishes at this time of year. They include tangogi soup (dog meat soup) and samgyetang (insam-chicken soup), etc., among which tangogi soup is a distinctive national dish preferred by our people during the summer heat. “Tongguksesigi”, compiled before 1849, says that tangogi soup was known across the country as the best dish during the summer heat. In general, both the early and mid dog days last ten days each. There is also a year where the mid dog days last twenty days, which is said to have the prolongation of the late dog-day period.
Our people have regarded eating hot tangogi soup mixed with boiled millet or white rice in a sweat as the best invigoration. Therefore, tangogi soup was widely known as a nourishing soup that stimulates the appetite lost by the summer heat and provides nutrients to the weak constitution.
The folk games enjoyed by our people in July are koni game and ball-throwing.
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