Jo Nov 23, 2024
Currently, redox flow batteries are the most promising candidates for renewable energy storage in the field of MW-scaled electrical energy storage technologies, among which vanadium redox flow batteries (VRFBs) have advantages of wide application range, low maintenance cost, strong load balancing capability, long cycle life, etc.
In VRFBs, electrolyte is one of the important components, which has a significant impact on device performance and cost.
During the continuous electrolyte preparation, the vanadyl sulfate (V(IV)) solution from the mixing reactor is continuously in contact with the cathode of several cascaded cells, and the V(IV) solution is partially reduced to the V(III) solution in the first cell, and then completely converted to V(III) in the final cell. During electrochemical reduction, a solution of V(IV)/V(III) ratio 1:1, i.e., a neutral solution and a solution V(III) from the final cell, is used for VRFBs. Therefore, the real-time analysis of each vanadium species in the electrolyte preparation process is essential and of great significance.
Potentiometric titration is commonly used to directly determine vanadium electrolyte concentration. This method is not suitable for online monitoring because it is time-consuming and requires experiments. Recently, digital image-based methods have been selected for quantitative analysis in analytical chemistry. Moreover, the use of digital image analysis has attracted considerable attention in studying electrochemical processes with color changes. Digital image acquisition is a non-contact, non-invasive, cost-effective technique and it can overcome certain problems in classical spectroscopic analysis such as reduced and scattered spectral signals. These analytical methods have advantages such as low cost, high analytical accuracy and short analysis time.
Jon Sang Mo, a researcher at the Faculty of Chemical Engineering, has proposed a digital image-based analytical method to determine the concentration of vanadium species (V(IV)/V(III)) in the process of vanadium electrolyte preparation. Since this method is simple in procedure and less time-consuming compared to other analytical methods, it could be applied to real-time analysis in the process of electrolyte preparation.
You can find the details in his paper “Analysis of vanadium species(V(IV)/V(III) in the electrolyte manufacturing process for vanadium redox flow battery using digital image” in “Journal of Electroanalytical Chemistry” (SCI).
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Jo Nov 23, 2024
As the demand for flexible and wearable electronic devices with stand-alone power sources is increasing, the development of flexible and lightweight photovoltaic devices that can be integrated directly into products of complex shapes is becoming a major direction of photovoltaic applications.
The flexible dye solar cells (F-DSCs) usually consist of a photo anode coated with a dye-sensitized semiconductor layer on a flexible transparent conductive substrate, a counter electrode with a thin catalyst layer on a conductive substrate, and an electrolyte commonly containing iodine-based redox couple (I-/I3-).
Usually, transparent conductive plastic films (tin oxide indium/polyethylene naphthalate-ITO/PEN) or flexible metallic materials (titanium foils, titanium wires, titanium or stainless steel mesh, etc.) are used as flexible substrates.
Photo anodes using transparent conductive plastic film substrates cannot undergo high temperature (higher than 450℃) annealing to remove organic residues from the nanostructured film, and cannot form chemical bonds between the conductive layer and the semiconductor film, thus causing low charge transport and collection. Flexible photo anodes based on metal foil substrates can improve charge transport and collection by applying high temperature annealing treatment.
The metal film substrate is mostly titanium films or wires, and their high cost limits their wide application.
Therefore, it is necessary to develop new fabrication techniques based on low-cost substrates such as normal glasses, plastic and paper in order to replace the above substrates.
Jon Sang Mo, a researcher at the Faculty of Chemical Engineering, has proposed a novel structure of F-DSCs using TiO2 Nano paper as a flexible substrate and porous Ti BCE composed of metallic titanium particles as a collector electrode.
The PCE of F-DSCs with TiO2 Nano paper substrate and porous Ti BCE reach 4.38% under AM1.5G and 100mW·cm-2 simulated solar irradiation.
You can find more information in his paper “Flexible dye solar cells with TiO2 nanopaper and Ti back contact electrodes” in “Journal of Saudi Chemical Society” (SCI).
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Jo Nov 22, 2024
Since the first mobile phone for civilian use was invented in 1973 by Martin Cooper, mobile phones have become essential for daily life and they have been most commonly manufactured. The use of mobile phones and their upgrading speed have been increasing rapidly in recent years.
In addition, the product life cycle of a mobile phone has reduced considerably and its service life is currently in the range of three years. Thus, e-waste from end-of-life (EOL) mobile phones (hereinafter referred to as e-waste) is increasing two to three times faster than that from other products.
Primary constituents of e-waste from end-of-life (EOL) mobiles are glass, metal and plastic. Thus, the quality of e-waste recycling is dependent upon individual indicators like plastic recycling and recovery of metals which in turn are dependent upon various other attributes.
The problem of comprehensively evaluating quality for each system in a set of similar EOL mobile phone recycling systems has not been addressed in the literature.
Ri Ji Hye, a researcher at the Faculty of Management of Industrial Economy, has proposed a method for accomplishing this objective by using Multi Attribute Global Inference of Quality (MAGIQ) technique.
The results of the case studies showed that the application of this technique can provide decision makers with a clear picture on the quality of various recycling systems under evaluation.
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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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