Jo Nov 20, 2023
Recently, rare earth elements (REEs) are widely used in special material science, and therefore, preparation and application of REEs have been rapidly developed.
La, Sm, Pr and Nd among REEs are common additives. It is important to determine amounts of them in materials since they change the mechanical and electronic properties of materials.
Kim Pyong Hun, a section head at the General Assay Office, has studied atomization process of La, Sm, Pr and Nd by GFAAS. He also investigated the possibility of preconcentration of REEs by selective evaporation of matrix, and found proper atomization and pyrolization temperatures. Then, he made sure the use of chemical modifier and mini-flow of internal gas at atomization step resulted in relative enhancement in sensitivity.
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Jo Nov 18, 2023
Organic and inorganic compounds have been used as a modifier for enhancing bonding force and strength of sodium silicate sand at room and high temperatures. Sodium silicate is generally used as an inorganic binder for producing molds and cores which are hardened by CO2 or ester.
The additive amount of sodium silicate should be decreased by raising its binding capacity to improve the strength and collapsibility. Therefore, it is necessary to refine colloidal particles and change the structure of sodium silicate by modifying it.
Many studies on modification of sodium silicate have been concentrated on application of organic compounds with functional group.
O Kwang Hi, an institute head at the Faculty of Materials Science and Technology, has modified the size of colloidal particles of sodium silicate by sodium phosphate. Then, he has measured and compared the sizes of colloidal particles of modified and unmodified sodium silicate by using SEM. After that, he has observed the change of crystal of modified and unmodified sodium silicate by XRD.
For modification, he set the pressure at 0.4~0.5MPa, time at four to five hours and additive amount of modifier at 4%.
The main conclusions of his study are as follows:
Firstly, the heating temperature of sodium silicate core modified by sodium phosphate is 760~1 400℃ for cast iron and steel castings with wall thickness of 8 to 60mm, and after being heated at the temperature of 800~1 200℃ the retained compressive strength and the knockout energy of the modified sodium silicate sand are about 1/3 and about 1/2 lower than those of unmodified one.
Secondly, when the modified sodium silicate is heated and cooled, collapsibility of the mold is improved due to the difference in the shrinkage stresses between silicate glass and phosphate glass.
Thirdly, when sodium phosphate is added to sodium silicate as a modifier, Na2O-SiO2 binary system is changed into Na2O-SiO2-P2O5 ternary system, and net colloidal structure is formed to enhance the binding strength as a result of interaction between phosphate tetrahedroid and silicate tetrahedroid.
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Jo Nov 17, 2023
Practical application of manipulators needs determination of their dynamic errors to guarantee positioning accuracy.
Many researchers determined kinematic errors of Delta parallel manipulators, but not dynamic errors.
Pang Thae Jin, a researcher at the Robotics Institute, has established a new method for dynamic error determination of a Delta parallel manipulator with three actuators using a deformation model.
He wrote an algorithm based on the kinematic and dynamic models and developed a program for obtaining dynamic errors of a Delta parallel robot, using MATLAB software.
His method can be applied to construction of control systems for error compensation of complicated manipulators of different shapes.
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Jo Nov 15, 2023
Among the valuable cultural legacies created by our nation is Sungryong Hall in Central District, Pyongyang City.
Sungryong Hall is a shrine first built in the fifteenth century during the feudal Joson dynasty. It was originally used for a memorial service for King Tangun, the founder of Ancient Joson, which was the first ancient state in our country’s history. Later, memorial services for King Tongmyong were also held here. The present building was rebuilt in the eighteenth century.
The original hall was made up of a main hall, two-kan servant’s quarters to the east and west with two one-kan doors each and a three-kan gate. Most of them were destroyed by the Japanese imperialist aggressors, with only the main hall and the gate survived. During the Fatherland Liberation War, they were badly damaged by the US imperialists’ barbarous bombing raids. Sungryong Hall is now restored to its original state. It is a valuable architectural legacy reflecting the architecture of the days of feudal Joson dynasty.
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Jo Nov 14, 2023
Al-Si alloys are widely used in producing precise wear-resistant parts, such as air condition compressors, automobile engine pistons and cylinder bodies in automotive industry and machine-building industry due to the best cast ability among cast aluminum alloys. Especially, hypereutectic Al-Si alloys are rich in silicon. Therefore, they have some advantages such as small coefficient of heat expansion, good resistance to wear, high dimensional stability and lower casting cost.
At the same time, they have some disadvantages of lowering mechanical properties by primary crystal silicon as rough polygon or piece layers unless modified treatment is not enough in crystallization process because of high content of silicon.
Al alloys containing a trace of rare earth metal have high strength, hardness, wear resistance, corrosion resistance and electrical conductivity.
Preceding researches were mainly conducted on the effects of rare earth metal on the mechanical properties of Al-Si alloys.
Ri Hyon Mo, a researcher at the Faculty of Metal Engineering, has investigated the effects of Al-10RE master alloy as grain finer on the tensile strength, elongation percentage and resistance to wear of AiSi19Cu2주. Al-10RE master alloy was used as grain finer of AiSi19Cu2주.
The tensile strength, elongation percentage and resistance to wear of Al-Si hypereutectic cast alloy increase with increase in additive amount of Al-10RE master alloy up to 5%, but they decrease over 5%. After heat treatment, the tensile strength and elongation were 296MPa and 0.84%, respectively, when the additive amount of Al-10RE master alloy was 5%. They increase by 24.4% and 44.8% respectively more than AiSi19Cu2주 without addition of Al-10RE master alloy.
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Jo Nov 11, 2023
A changsaenap is a peculiar woodwind instrument based on a saenap (a Korean brass wind instrument). It was born in the course of development of national instruments under the wise leadership of our Party.
It satisfactorily preserves the features of a saenap in terms of shape and sound quality, supporting the characteristics peculiar to our national instruments.
On the pipe are some finger holes for whole tones and half tones, and some keys.
Compared to a saenap, a changsaenap makes a wider range of and softer sounds.
Such characteristics make execution of folk trills, staccatos, vibratos, etc. successful. It is widely used as a solo instrument.
In addition, it highlights national characteristics in orchestral music and ensembles, and it is effective in playing appealing pieces.
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