Jo Oct 18, 2024
Silicon carbide powder, complexed in metal matrix, has been widely used to manufacture various tool steels by casting and powder metallurgy as it has excellent hardness, abrasion resistance and heat resistance. However, silicon carbide powder, whose phase is like a kind of ceramic, has low wettability with metal, so when it is complexed in metal matrix, the microstructure of complex material around the particles of silicon carbide is changed, leading to the significant fall in the life of tool steels.
To overcome these disadvantages, there have been some researches to prolong the life of tool steels and to manufacture various functional complex materials by coating the surface of silicon carbide powder with metals such as nickel or copper by electroless plating based on the chemical reaction of oxidation and reduction.
However, there are no reports on the quantitative observation of nickel plating rate and the control of plating thickness on the basis of the reactions taking place during electroless plating on the surface of silicon carbide powder.
Jang Ryong, a researcher at the Faculty of Chemistry, experimentally studied the effects of amount of nickel salt and reducing agent on nickel-plating rate and thickness during the electroless nickel plating on the surface of silicon carbide powder.
He found that during electroless nickel plating on the surface of SiC powder with particle size of 42㎛ the amount of nickel salt should be as small as possible (mass of NiCl2·6H2O is 16.14g in 800mL solution) and the amount of reducing agent NaH2PO2·H2O should be more than 3 times that of nickel salt substance.
Laser Scanning Microscope (LSM) images of non-plated and plated SiC powders (0.5㎛ in thickness) showed that black metallic nickel was evenly coated on the surface of silicon carbide powders.
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Jo Oct 15, 2024
The environmental problems such as air pollution by exhaust gases and global warming are now growing worldwide, and the development of electric vehicles (EV) as a means to solve these problems is gaining attention. Recently, the development of low-volume, energy-density and high-power batteries and high-performance, low-cost rare-earth permanent magnets, and the rapid development of power electronics technology have made the development of electric vehicles more intensive and accelerating.
Vehicle acceleration, single-charging travel distance and maximum slope-climbing capability need to be increased to encourage wide use of electric vehicles like traditional fuel vehicles.
In many references, different driving modes to analyze the dynamic motion characteristics of an electric vehicle were considered and the effects of parameters on the performance of a vehicle and energy consumption were analyzed on MATLAB/SIMULINK.
Ri Tong Hyon, a researcher at the Faculty of Electrical Engineering, studied the mathematical model of an electric vehicle to analyze and simulate its static and dynamic motion. On this basis, he confirmed the technical specifications of a traction motor.
First, based on the simulation analysis of static and dynamic motion, he investigated the traction force characteristics, the driving resistance characteristics, the speed-torque characteristics of the traction motor and the distribution of the operation points of the traction motor in different driving modes. Then, he determined the technical indices including the power, torque and rotational speed of a traction motor with high acceleration performance.
The effectiveness of the proposed method was verified through the simulation.
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Jo Oct 14, 2024
Manganese and its compounds are widely used in various fields of the national economy such as ferrous and nonferrous metal industries, chemical and electrical industries, glass and ceramic industries and agriculture due to their unique physicochemical properties. This leads to the gradual depletion of high-grade manganese ores and, hence, growing concern is focused on the treatment of low grade manganese raw materials. Pyrometallurgy processing of low-grade manganese raw materials consumes a great amount of energy and produces huge waste volume and low yield. Therefore, it is suitable to process such raw materials by hydrometallurgy method.
Sulfuric acid is mainly used as a leaching solvent in the hydrometallurgy process of manganese raw materials. This leaching solution of sulfate contains different impurities such as Fe, Co, Ni, P and As. These impurities reduce the quality of manganese products and affect the technical and economic index of the production process. Hence, it is necessary to remove all the impurities in the liquid in order to obtain the desired product. The impurity which is found in largest quantities is iron. How to remove the iron in high concentration has a considerable effect on process yield, cost of production, working conditions and environments.
Jon Yong Nam, a researcher at the Faculty of Metal Engineering, has proposed a jarosite precipitation and an absorption method by manganese concentrate for removing iron from manganese sulfate leach, and comprehensively analyzed the basic experimental results for their applications.
In the synthesizing process of (NH4)2Fe6(SO4)4(OH)12 using MnSO4 solution, several factors including reaction temperature, reaction time, pH of reaction, seed addition, etc. have significant effects on the removal rate of Fe3+, among which the reaction temperature is the most prominent. The appropriate reaction conditions are 95℃ of reaction temperature, two hours of reaction time, 2.5 of pH of reaction and 15g/L of the addition amount of seed. After Fe in the solution is basically removed by the jarosite method, the remaining iron in the solution can be removed by Mn concentrate absorption. The absorption reaction condition is 65℃, 6.5~7 of pH, 6~8g/L of addition amount of Mn concentrate, and at this time, the Fe content in the solution can be ensured below 0.03g/L.
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Jo Oct 13, 2024
It is difficult to ensure ideal symmetric conditions during hot plate rolling, so rolled plates may bend upwards or downwards. The factors affecting the plate curvature are temperature difference, roll diameter difference, rolls speed mismatch, frictional difference, reduction rate, ingoing thickness, inclination angle, etc.
In the single strand mill, the difference in the height of the upper parts of the lower roll and the breast roll is fixed. So, during multi-pass rolling, the plate sometimes faces inclined entry. Reprocessing of the work roll also causes the difference in the roll diameter. Therefore, it is very important to determine the admissible roll diameter ratio that causes very narrow range of plate curvature for normal rolling.
Ri Chun Ho, a researcher at the Faculty of Materials Science and Technology, investigated the influence of the inclination angle of the plate on strip curvature during the 7 passes of reversing rougher at the hot mill when the plate enters with inclination, by using the three-dimension finite element analysis software, DEFORM-3D. Based on this, he determined the range of admissible roll diameter ratio that leads to the very narrow range of plate curvature when the plate enters with inclination.
He found that the roll diameter ratio of reprocessed work rolls is not allowed to exceed 1.067.
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Jo Oct 11, 2024
Coal is a main energy resource and many households in our country use honeycomb briquettes made of coal for heating and cooking. In summer honeycomb briquettes are mainly used as fuel for cooking. But they reveal some shortcomings such as difficulty in ignition and low combustion efficiency due to the need for high ignition temperature.
The most important thing is to reduce the time and energy needed for ignition of honeycomb briquette as much as possible, and to raise the combustion rate up to the level of gas combustion for instant cooking. 150 to 200 grams of wood sticks are needed for ignition of honeycomb briquettes. If the calorific value of wood is 16MJ/kg, as much energy as 2 400 to 3 200kJ is consumed for ignition alone. What is more, a large amount of flame and harmful gases are released due to the difference in the activation energy between coal and biomass, which pollutes the environment.
Therefore, many researchers have conducted studies to lower the ignition temperature and raise the combustion rate by lowering combustion activation energy of coal. To this end, they added combustion additive to coal or mixed coal and biomass. To prevent the release of much flame during ignition with wood sticks, some researchers have developed double-layer or multi-layer ignition honeycomb briquettes to be ignited with a sheet of paper or a match stick. The problem is that if biomass like raw sawdust is added to the upper sides of briquettes as it is, it produces smoke and exerts bad influence on coking power.
Jon Chol, a researcher at the Faculty of Mining Engineering, on the basis of the analysis of biomass ignition characteristics for its size, has studied the ignition and combustion characteristics of upper side ignition honeycomb briquettes and determined appropriate crushing size and blending rate of biomass.
The results showed that the upper side ignition honeycomb briquette added with biomass has ignition time of two to three minutes on average, combustion time of 75 minutes and combustion rate of 156.12g/min, and that the most appropriate biomass crushing size is 125㎛.
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Jo Oct 10, 2024
Fishing started in Korea thousands of years ago.
Spears and hooks made of bone and stone, and sinkers made of broken earthenware are often found from the Neolithic remains in all parts of the country that have been known so far.
These fishing tools demonstrate that the Korean ancestors started fishing before the Neolithic Age.
Fishing tools developed into various types through a long course of history.
According to the archaeological discoveries, it is guessed that a wooden sailing boat must have come into being in the Bronze Age.
A big heavy sinker for deep sea fishing, an implement for spearing a fish caught in the net, scallop shells in the deep sea, etc. were found from the Chodo Remains (remains of the Bronze and Iron Ages) in Rason City. All these prove that fishing on a sailing boat in the deep sea already started in this period.
The Korean people developed the fishing method in a more efficient and diverse way over a long period of time, considering the nature and habitat of fish. They also devised a way of pickling, freezing and drying the fish for effective storage and processing.
From olden times, the Korean people have steadily developed fishery while fishing in conformity with the nature and terrain of the country.
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