Jo Mar 6, 2025
Zeolites have been widely used in various industrial fields including the chemical industry due to their unique catalytic properties and excellent adsorption and ion exchange capabilities, and there is a constant interest in developing zeolites with different performances, reducing their production costs and making their synthesis easier.
ZSM-5 zeolite, synthesized in the early 1970s, has a large specific area and high thermal and mechanic stability, and it has a porous structure consisting of alternating three-dimensional straight pore channels and Z-type pore channels, which makes it widely used in various fields, such as the industry of fine chemicals, oil chemistry, environmental protection, etc. Especially, it has been used as a catalyst, a molecular sieve and an adsorbent in the chemical industry.
ZSM-5 zeolite is usually synthesized by hydrothermal synthesis using silica raw materials, alumina raw materials and organic templates as synthetic materials. Aluminum sulfate, aluminum nitrate and sodium aluminate are widely used as raw materials of alumina source for ZSM-5 zeolite synthesis, while silica sol, water glass, etc. are widely used as silica source. In addition, quaternary ammonium salts, alcohols, amines and amino alcohols are used as organic templates. The choice of an organic template will determine the cost of ZSM-5 zeolite, which limits the industrial production of ZSM-5 zeolite.
Sin Hyok, a researcher at the Faculty of Chemical Engineering, has proposed a method of synthesizing ZSM-5 zeolite using water glass, aluminum sulfate and triethylamine as a silica source, an alumina source and a template, respectively, and determined the optimum crystallization condition for synthesizing ZSM-5 zeolite using such materials as mentioned above.
He defined the molar ratio of raw materials in aluminosilicate gel as 6Na2O:50SiO2:1Al2O3:1 300H2O:10C6H15N and performed hydrothermal crystallization at 100-150℃ for 30-42 hours. Then, he determined the optimum crystallization temperature and time, with relative crystallinity of 95% and solid product yield of more than 0.9.
He found that in a certain temperature range, the relative crystallinity and solid product yield increased with increasing crystallization time.
The proposed method is a new approach to prepare ZSM-5 zeolite from commercially accessible and relatively inexpensive raw materials.
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Jo Mar 5, 2025
There are many precious and beautiful living monuments in the DPRK. Phojung Pine Tree is one of them.
It is in Phoha-ri, Myongchon County of North Hamgyong Province.
It is believed to have been planted around 1630.
People in this area also call it “umbrella pine” as it resembles an umbrella and looks so beautiful and exquisite from everywhere.
It is 12 meters tall, with the root collar of 3.2 meters round, the chest-height of 2.8 meters round and the canopy of 15 meters from east to west and 18 meters from north to south.
It is growing straight up to the height of five meters where the branches spread far and wide to bend downwards near the ground, forming a great canopy resembling an umbrella.
What is special about this kind of tree is its small pinecones with no seeds.
This old tree of unique shape and attractive appearance is a precious living monument of scenic and academic significance.
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Jo Mar 3, 2025
Wastewater treatment process (WWTP) is difficult to control because its biological, physical and chemical phenomena are complex and they are interrelated and highly nonlinear.
Recently, model predictive control (MPC), which employs a prediction model of the plant to optimize future plant behavior, has been a popular approach for WWTP. Since WWTPs are multivariable, multi-objective optimization of MPC is required.
Kim Kyong Jin, a researcher at the Faculty of Automation Engineering, has proposed a nonlinear multi-objective MPC (NMMPC) to realize a multivariable control for WWTPs.
The proposed multi-objective optimal control comprises a self-organizing radial basis function neural network (SORBFNN) identifier, a model predictive controller and a multi-objective optimization method. He developed the SORBFNN as a model identifier for approximating the online states of dynamic systems. The solution of the multi-objective optimization is obtained by a gradient method which can shorten the solving time of optimal control problems.
The experiments have revealed that the proposed control technique gives satisfactory tracking and disturbance rejection performance for WWTPs.
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Jo Mar 2, 2025
Analysis of CO2 is very important in several fields including chemical industry as well as estimation of environment, monitoring of disasters, etc.
Laser spectrum technology is effective for minimal gas analysis in the fields of environment and industrial measurement. Coherent light source which can be adjusted to the narrow width of spectrum can detect an absorption line of the matter and avoid interference of signals caused by other kinds of matter.
Narrowband filter is a major element for separating fine spectrum including gas analysis. Narrowband filter for breaking broadband has a complex structure of over 60 layers. The most widely-used narrowband filter is Fabry-Perot interferometer. This filter, which has a spacer between two reflective layers, forms interference maximum for the beam that satisfies the resonance condition according to the thickness of the spacer, thus ensuring sharp spectrum transmission.
In order to analyze CO2 in a gaseous mixture, Kye Song Chol, a researcher at the Faculty of Mechanical Science and Technology, has designed a multi-layer system of the filter for selectively filtering the absorption line of CO2 gas and cutting absorption lines of other air components.
As common Fabry-Perot narrow band filters have high spectral selectivity, he designed a double Fabry-Perot filter, which has low spectral selectivity and high transmittance at reference wavelength. For broadband cutoff, he combined a double Fabry-Perot filter and a broadband filter of symmetrical period structure, thus ensuring the necessary spectral characteristics and improving manufacturability. To increase the transmittance of band on which CO2 absorption line is located, he applied the equivalent theorem of a symmetrical period coating system and the index distribution of antireflection.
This filter consists of a double Fabry-Perot narrowband filter and a wideband filter placed on both sides of the Ge substrate, which can provide the required spectral characteristics while avoiding the complex structure of more than 60 layers of the conventional one.
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Jo Mar 1, 2025
In our country, March is the time when spring sets in.
Seasonal divisions in March are kyongchip and chunbun.
Kyongchip, which literally means the time when hibernating worms start to wriggle, awakened by the melting ice and the rain with thunder, falls around March 5 by the solar calendar.
Chunbun, which means the period in the middle of spring, falls around March 21 by the solar calendar. In this period, there is almost no difference in the length of the day and the night, and although it often blows hard, the weather gets mild and the ground thaws out.
Around kyongchip and chunbun, the Korean people used to mend the fences and spring-clean houses and surroundings to clear away the traces of winter before starting farming. In addition, they liked making delicious food with edible herbs coming out green and fresh in the fields to enjoy the flavor of spring.
The typical herbs are shepherd’s purse and wild garlic.
They also used to pick various kinds of medicinal herbs for storage and do peasants’ dancing and singing to add a zest to farming, hoping for a good harvest.
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Jo Feb 28, 2025
Speckle is one of the main obstacles to the application of self-mixing interferometers into practice.
Self-mixing model reflecting speckle is of great theoretical and practical significance in self-mixing interferometry.
Ho Kwang Myong, a researcher at the Faculty of Physical Engineering, has suggested an improved model for a clearer explanation of the effect of speckle on self-mixing signals, and investigated the mechanism of feedback coefficient intensity variation induced by speckle and the effects of the surface orientation on the signals.
First, he built an improved model by replacing the output mirror reflectivity with amplitude feedback fraction in an external cavity and provided equations to calculate the amplitude feedback fraction.
Then, he proved through simulations and experiments that the irregular fluctuation of the speckle affected self-mixing signal is mainly due to the orientation change rather than the longitudinal displacement.
For further information, you can refer to his paper “Improved self-mixing model reflecting speckle” in “Applied Physics B” (SCI).
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