Jo Nov 21, 2024
Twin-roll continuous casting is a near-net-shaping casting technology that possesses advantages of short processing time, low investment cost, and low energy consumption. Thus, this technique has been attracting great attentions of steelmakers of the world as one of the new technologies for the steel industry, which is developing with the tendency of low energy consumption, short processing time and low manufacturing cost.
The principle of twin-roll continuous casting is based on pouring the molten metal into the gap between two rotating water-cooling cylindrical copper rolls. The metal solidifies just before reaching the bite of the rolls and then is rolled while passing through the rolls. Correctly defining the height of the kiss point, where two solidified layers of molten metal are met between twin-rolls, has a great influence on calculating the force on the twin-roll and improving the quality of cast strips.
Kim Jong Min, a researcher at the Faculty of Materials Science and Technology, has studied the effects of the height of a molten pool, casting speed and the temperature of a twin-roll on the height of the kiss point for a twin-roll continuous caster with a diameter of 1 000 millimeters.
To determine the height of the kiss point, he simulated temperature distribution at the molten pool between twin-rolls by commercial simulation software ProCAST. Based on the mathematical modeling, he studied the effects of the height of a molten pool, casting speed and the temperature of a twin-roll on the height of the kiss point.
The results showed that with increase in the height of a molten pool and decrease in the casting speed and the temperature of a twin-roll, the height of the kiss point increases.
Thus, the casting speed, the height of a molten pool and the temperature of a twin-roll should be properly selected based on the thickness of the cast strip to guarantee the exact height of the kiss point.
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Jo Nov 20, 2024
Middle Carboniferous System in the valley of Taizi River, eastern Liaodong Province, China, has been called “Benxi Formation” and recognized as being correlated with Hongjom Formation on the Korean Peninsula.
Kim Myong Hak, a section head at the Faculty of Earth Science and Technology, has made a biostratigraphic comparison of Hongjom Formation in the Pyongyang area with Carboniferous System in the valley of Taizi River, eastern Liaodong Province. In addition, he has carried out palaeontological and stratigraphic studies of the upper part of Mantal Formation of this area to provide new insights into the stratigraphic problems.
The results are as follows.
The stratum now recognized as Hongjom Formation in the Pyongyang area is correlated with Tianshifu Formation and Benxi Formation that the former “Benxi Formation” in the valley of Taizi River, eastern Liaodong Province, is subdivided into.
The stratum containing plant fossils in the upper part of Mantal Formation is regarded as an independent one that extends more than 20 kilometers.
The fossil assemblage of this stratum differs from those of Mantal Formation and Hongjom Formation. Based on the lithological and paleontological characteristics of this stratum, it can be correlated with Muyuzi Formation (late Early Carboniferous) in the valley of Taizi River, eastern Liaodong Province.
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Jo Nov 19, 2024
Among rare earth elements (REEs) deposits of sedimentary type is a phosphorite deposit containing REEs, which are distributed in DPR Korea, China, Algeria, Tunisia, Pakistan, Israel, Syria, Morocco, Canada, etc.
The phosphorites of the lower Cambrian strata are relatively widely distributed in Yunnan Province, Guizhou Province, Jiangxi Province, Zhejiang Province and Jiangsu Province of China, in which the geochemical characteristics of P2O5 and REEs have been studied in detail. Most of the studies have been focused on elemental geochemistry and sedimentary environment. However, they have only dealt with the characteristics of distribution and variation of REEs in the basal phosphorite of lower Cambrian but not with overlying strata.
Kim Kwang Chol, a section head at the Faculty of Earth Science and Technology, has investigated the REE content and its distribution characteristics of the phosphorous siltstone developing in the middle part of the lower Cambrian strata.
He studied the characteristics of mineral composition and REE composition of sedimentary rocks of the lower Cambrian strata of Hwangju-Yonthan area in the DPR Korea by microscopy observation, chemical analysis, ICP-MS analysis, XRD analysis and infrared ray (IR) spectroscopy, etc. The result has shown that the phosphorous siltstone in the middle layer contains appreciable amounts (generally from 340.0 to 1 105.6ppm) of REEs. This phosphorous siltstone layer is more than 15-21 meters thick, over several hundred meters long in the strike extension, and has high HREE content (HREE/ΣREE ratio is generally from 0.232 9 to 0.394 7).
This result seems to have valuable applicability, especially in the search for and evaluation of HREE deposits in all areas where the low Cambrian strata develop.
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Jo Nov 17, 2024
With the rapid development of plasma technology, the agricultural sector has recently introduced a wide application of plasma activated water with the potential to increase the germination, growth and grain yield of crops.
Atmospheric pressure cold plasma in the gas phase contains active species such as charged particles (electrons and ions), ozone, atomic oxygen, superoxide radical, hydroxyl radical, nitrous oxide radical, and nitrous oxide radical. When these gaseous active species dissolve in the liquid, a dynamic chemical reaction takes place to form liquid active species. The resulting chemically active species, with short or long lifetime, can achieve the overall biological effect associated with plasma activated water.
It was previously confirmed that nitrate, nitrite and hydrogen peroxide (H2O2) as stable and long-lived active species are detected in plasma activated water. Therefore, quantitative detection of H2O2 is important for considering the biological effects of crops associated with plasma activated water.
The generation of various active species by plasma flow depends on various parameters such as plasma power type, carrier gas species, electrode structure, applied voltage, voltage polarity, processing time, gas flow rate, solution volume, distance between electrode and liquid surface, solution composition, pulse duration, etc.
The use of air as a plasma working gas has many advantages such as safety, low cost and convenience for operation of the device.
An Song Il, a researcher at the Nano Physics Institute, has conducted an experiment by choosing two types of discharge electrode structures in which air is in contact with water as a working gas, and compared the characteristics of the active species produced in water.
The result showed that the concentration of the total active species in the plasma activated water by mode 1 is higher than that of mode 2.
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Jo Nov 15, 2024
Real-time analysis in the chemical industry is becoming increasingly important as science and technology develops. The reality that real-time analysis is an essential tool for process automation and remote control is encouraging the introduction of new analytical systems more convenient and more accurate.
The establishment of analytical systems based on chemical image analysis has attracted great attention in the fields of process automation, agriculture, biology and medicine as well as analytical chemistry worldwide for its great prospect of application in process analysis.
The amount of nickel in plating solution is analyzed by photoelectric colorimetry, complex titration, gravimetry, polarography, etc. However, the chemical analysis of these nickel plating solutions is only possible in laboratories and limited in large-scale processes due to the manual work throughout the process.
Kim Yong Ok, a researcher at the Faculty of Chemical Engineering, has proposed a methodology for applying AI technology to chemical image analysis of nickel plating solutions.
First, she performed the preprocessing of solution images using dynamic contrast enhancement technique and constructed an extensible private function for capturing representative pixels from the preprocessed image.
Next, she developed a mobile application to establish a nickel analysis system in nickel plating solution by using deep learning. In particular, she built a model that underwent mechanical learning into Android applications so that all processes from photography to analysis could be carried out in a single program.
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Jo Nov 14, 2024
Recently, laser isotope separation has emerged as the most practical method for isotope separation compared to other separation methods, and research into it has been conducted intensively. There are several methods for laser separation, among which atomic vapor laser isotope separation is accepted as a promising method for both wide range of applications and possibility of expansion.
In this method, the first step of separation process is atom vapor and collimating. If the vapor source is heated to the target temperature under complete vacuum conditions, feed metal is melted to liquid state and starts evaporating. According to the temperature of vapor source, the rate of evaporation and vapor pressure of feed metal are controlled, which adjusts the atomic density of collimated atomic beam. At the laser pumping region, the atomic density of atomic beam is critical to the absorption cross section of laser beam.
Kang Chol Jin, a researcher in the General Assay Office, simulated the distribution of lithium vapor as a function of the length-to-diameter ratio of the source nozzle for laser isotope separation of lithium, and experimentally determined the atomic density distribution of lithium atomic beams in the collimated region.
It was found that when the heating temperature of the lithium vapor source was kept at 500℃, the atomic density near the nozzle central axis increased relatively rapidly with increase in the length-to-diameter ratio of the outlet nozzle, i.e., the atoms flying at an angle similar to the central axis of the tube flew almost linearly out of the nozzle.
According to the calculations, when the L/D value of the nozzle at 500℃ was 10 and the diffusion angle of the atomic beam was 10°, the collimation efficiency was above 46%.
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