Jo Feb 6, 2026
PTC (positive temperature coefficient) thermistors based on BaTiO3 semiconducting ceramics are important devices for ferroelectric materials.
Due to their great temperature coefficient of resistance, barium titanate and its related compounds are ideal candidates for producing various PTC components. Particularly, Ba1-xSrxTiO3(x=0~1) ceramic material-based PTC thermistors have nonlinear characteristics around the Curie point, which can be enhanced by the addition of some minor impurities such as Cu and Mn.
Jo Myong Chol, a researcher at the Institute of Semiconductor, has investigated the effects of Mn addition on the dielectric properties and microstructure formation of BaTiO3-based ceramic chips and the effects of heating rate on PTCR response of barium-strontium titanate (BST) ceramics doped with Mn dopants.
Mn addition works as a sintering agent, which influences the densification behavior of the overall ceramic material. The dielectric constant increases to as high as 5 800 (at 25℃) and the dielectric loss decreases by 1% when Mn-content is added properly. This shows that the phase formation, density, microstructure and electrical properties of co-doped BST ceramics containing sintering additives are strongly affected by heating rate.
The highest densification during sintering occurs at the heating rate of 5 or 20℃/min. There is a general trend of decrease in effective resistivity with increasing heating rate, which could be attributed to the decrease in grain size. However, when the heating rate went from 5 to 20℃/min, there was a slight increase in resistivity, which may have been due to the increased proportion of crystallized secondary phases in the most rapidly heated sample, but the reasons for this are uncertain. Thus, it can be concluded that 3 and 5℃/min are the best heating rates for favorable PTCR effects.
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Jo Feb 3, 2026
From olden times, the Korean people have celebrated Jongwoldaeborum (lunar January 15) as one of the great folk holidays, and they made it a traditional practice to make several kinds of dishes including ogokbap, yapbap, laver-wrapped rice, nine kinds of seasoned edible grass, noodle, etc. and enjoy them on this day.
Ogokbap is boiled rice admixed with four other staple cereals.
The ingredients usually included five kinds of cereal―white rice, hulled glutinous millet, polished millet, hulled barley and adzuki beans, but the five kinds of cereal were not fixed. Here is a recipe for ogokbap.
First, adzuki beans are soaked in water.
Second, hulled glutinous millet and polished millet are washed.
Then, white rice, adzuki beans and hulled barley are boiled together. After some time of boiling, hulled glutinous millet and polished millet are placed upon the mixture.
Finally, the fire is weakened for enough steaming.
What is important is to add less water for glutinous rice than for common boiled rice.
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Jo Jan 30, 2026
Mixing is an important technique for improving product quality in various manufacturing processes. Various mixers are used in the mixing processes of many fields including iron works, food industry, cosmetics and construction.
Among various types of mixers, a twin spiral mixer has the advantage of small volume and continuous mixing. In a twin spiral mixer, the left and right spiral wings attached to two axes rotating in opposite directions alternately work by advancing the material in one direction. First, the left spiral wing rotates and contacts material particles, advancing them and sending some of them toward the right spiral wing. The right spiral wing then approaches the position where it can contact the particles. Next, the left spiral wing releases the particles, and the right spiral wing comes into contact with them, advancing them and sending some toward the left spiral wing. Thus, in the twin spiral mixer, mixing is achieved by a simple cross action of the spiral wings that send some particles toward each other. From this mixing principle, the mixing degree in the twin spiral mixer is determined by the number of wings that interact with particles. In addition, due to the single mode of mixing, the attainable mixing degree is not high, and therefore, the length of the mixer must be long inevitably to increase the mixing degree.
Generally, various methods of structural and working parameters optimization have been widely used to improve the performance of machines and equipment. However, these methods are not sufficient to fundamentally change the performance characteristics and they have certain limitations. In the twin spiral mixer, it is also difficult to achieve the improvement in the mixing degree by optimizing the structural parameters, since the mixing process is realized by a simple cross action of the spiral wings.
Ri Song, a researcher at the Faculty of Mining Engineering, evaluated the mixing degree by simulating the mixing process of a twin spiral mixer by DEM (discrete element method) and then, based on this, he proposed a plan of increasing the mixing degree by installing inverse spiral wings at regular intervals in a twin spiral mixer to change the mixing mode.
Comparing the mixing degree for the conventional twin spiral mixer and the twin spiral mixer with inverse spiral wings, it was 0.779 7 for the conventional mode, 0.801 3 for the 2:1 mode, 0.81 for the 3:1 mode and 0.790 7 for the 4:1 mode, which means the 3:1 mode was the best, and the outputs from simulations were 89.1W, 429.7W, 287.8W and 151.5W, respectively.
You can find more details in his paper “Study on improving the mixing degree of a twin spiral mixer by changing the mixing mode using inverse spiral wings” in “Journal of the Brazilian Society of Mechanical Sciences and Engineering” (SCI).
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Jo Jan 29, 2026
Scattering of elastic waves by inclusions or local topography in elastic half-spaces has been an important research topic in the fields of seismology, geotechnical engineering and acoustics. Analysis of the response and potential damage to underground structures under different kinds of loadings, especially strong earthquakes, is of great importance for the design and construction of deep underground tunnels.
The propagation and scattering of elastic waves around underground tunnels located under the surface of an infinite half-space have recently been studied using two methods: analytical method and numerical method.
The analytical method mainly focuses on the models of regular shape embedded in an infinite half-space. Although this method is only suitable for relatively simple and regular models, it has an advantage over the numerical method in revealing the essence of problems.
Ri Song Chol, a section head at the Faculty of Mechanical Science and Technology, investigated the influence factors on the dynamic response of a lined tunnel embedded in an inhomogeneous half-space under the conditions of incident SH waves.
He derived an analytical solution for the scattering of plane SH waves by a lined tunnel embedded in an inhomogeneous half-space by employing the complex function method and the conformal mapping technique. The analysis focuses on the treatment of straight and circular boundaries by proper coordinate transformation and by the conversion of the physical plane to the corresponding image plane.
For more information, you can refer to his paper “Analysis of the Influence Factors on the Dynamic Response of a Lined Tunnel Embedded in an Inhomogeneous Half-Space Subjected to SH Waves” in “Russian Journal of Nondestructive Testing” (SCI).
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Jo Jan 28, 2026
Slurry electroleaching, which produces manganese dioxide from low grade manganiferous raw materials, is noteworthy.
Studies on slurry electroleaching made a start in the latter half of 1960s. Since then, in-depth researches based on slurry electroleaching have been carried out on the treatment of galena, copper sulfide ores and manganese ores. As a result, many successes have been made so far.
However, few studies and applied cases with regards to the industrial method of processing low grade manganiferous raw materials (below Mn 10%) into manganese dioxide have been reported.
DPRK has little amount of Mn raw materials of over 20%. Instead, it has a great deal of wad clay. In order to meet the domestic demands, the problem of processing wad clay must be solved. In addition, the wad clay in our country contains lots of slime. According to some preliminary experiments, slime leaked into the anode diaphragm during the process of slurry-electroleaching, thus dramatically decreasing the rate of the content of manganese dioxide.
Based on the preceding research results, Jon Yong Nam, a researcher at the Faculty of Metallic Engineering, applied slurry electroleaching method (diaphragm electrolysis) to the low-grade wad clay (Mn 4~6%) which is deposited in the central region of DPR Korea in order to obtain high-grade manganese dioxide of over Mn 40%.
He observed the effects of the temperature, current density, ratio of liquid to solid (L/S), time and coagulant agent through the basic experiment on slurry electro leaching of the wad clay. He determined the optimum conditions as follows: current density 150~200 A/m2, temperature > 65℃, L/S = 10 : 1, time 1.1 times the theoretical leaching time and amount of the coagulant agent 50 g/t. Under these conditions, the leaching rate was above 95% and the content of Mn in anodic electrodeposits was 45%.
You can find the details in his paper “A Study on the Extraction of Manganese from Wad Clay by Slurry Electrolysis” in “Russian Journal of Non-Ferrous Metals” (SCI).
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Jo Jan 27, 2026
The arsenic bearing gold concentrate is known as refractory gold concentrate and the direct cyanide leaching produces very low gold extraction. It is because gold particles are extremely fine and encapsulated in sulfides (pyrite and arsenopyrite) and the exposure of gold particles is difficult by the mechanical method only.
Oxidation roasting, bio-oxidation and autoclave oxidation are used for pretreatment of refractory gold ore. The method of autoclave oxidation for this purpose has certain advantages in production cost and environmental protection, but it needs huge investment in equipment. Bio-oxidation is another choice in view of low cost and environmental friendliness. However, it is inefficient and too sensitive to the environment. Compared to these methods, oxidation roasting is brief in operation and the period of production is short. And the amount of treatment is large and the cost is low. In roasting processes, pyrite and arsenopyrite are oxidized to reduce the cyanide and dissolved oxygen consumption, and porous calcine is formed to increase gold extraction.
Two-stage roasting process is commonly used to pretreat arsenic bearing gold concentrate. The first stage is carried out in weakly oxidative atmosphere to release arsenic in the gaseous phase as As2O3. The second stage roast is performed in oxidative atmosphere to produce porous hematite.
Kim Yong Min, a section head at the Faculty of Metallic Engineering, investigated the effect of protective alkali and pH on gold extraction in the cyanide leaching process of two-stage roasting calcine of arsenic bearing gold concentrate.
The results showed that gold extraction was independent of protective alkali such as caustic soda, sodium carbonate and lime, and the effect of pH on gold extraction was obvious. If the pH of pulp is high, the arsenic concentration of cyanide leaching solution is increased to decrease gold extraction.
He also investigated the effect of arsenic concentration of solution on gold extraction. He found that when the leaching solution has no lead ion, the arsenic has no effect on gold extraction, but when the arsenic and lead exist in solution simultaneously, the effect of arsenic on gold extraction is remarkable.
For more information, please refer to his paper “Effect of Protective Alkali and pH on Gold Extraction in Cyanide Leaching Process of Two Stage Roasting Calcine of Arsenic Bearing Gold Concentrate” in “Russian Journal of Non-Ferrous Metals” (SCI).
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