• Korean Journal of Materials Research
• /
• v.31 no.8
• /
• pp.458-464
• /
• 2021

Tungsten disulfide (WS₂), a typical 2D layerd structure, has received much attention as a pseudocapacitive material because of its high theoretical specific capacity and excellent ion diffusion kinetics. However, WS₂ has critical limits such as poor long-term cycling stability owing to its large volume expansion during cycling and low electrical conductivity. Therefore, to increase the high-rate performance and cycling stability for pseudocapacitors, well-dispersed WS₂ nanoparticles embedded in carbon nanofibers (WS₂-CNFs), including mesopores and S-doping, are prepared by hydrothermal synthesis and sulfurizaiton. These unique nanocomposite electrodes exhibit a high specific capacity (159.6 F g^-1 at 10 mV s^-1), excellent high-rate performance (81.3 F g^-1 at 300 mV s^-1), and long-term cycling stability (55.9 % after 1,000 cycles at 100 mV s^-1). The increased specific capacity is attributed to well-dispersed WS₂ nanoparticles embedded in CNFs that the enlarge active area; the increased high-rate performance is contributed by reduced ion diffusion pathway due to mesoporous CNFs and improved electrical conductivity due to S-doped CNFs; the long-term cycling stability is attributed to the CNFs matrix including WS₂ nanoparticles, which effectively prevent large volume expansion.

• Journal of the Korean Chemical Society
• /
• v.52 no.1
• /
• pp.73-83
• /
• 2008

The purpose of this study was to investigate the types of conceptions of mixing phenomena related to dissolution and diffusion in high school students. The subjects of the investigation consisted of 108 students who took chemistry I course at 11th grade and 29 students who took chemistry II course at 12th grade. For this study, it was found that the many students had the alternative conception that chalk didn't dissolve in water because chalk was a nonpolar material. Most of the students understood the phenomena which carbon tetrachloride and water will not mix as the attraction conception. But many of the other students understood the phenomenon as characteristic of the materials such as difference of density. Many of the students understood the phenomenon of mixing ethanol and water constantly as ‘Attraction conception'. The phenomenon which is mixed ink and water was just accepted by the most students as the spreading of ink in water without understanding the reason of mixing. The phenomena of mixing iodine and carbon tetrachloride was understood as ‘Space conception' or ‘Attraction conception'. It could be inferred that the diverse alternative conceptions related to dissolution and diffusion phenomena were generated by the absence of entropy concept. Therefore, the explanations of science textbooks related to dissolution and diffusion phenomena need to change for students to understand them correctly.

• Journal of the Korean Society of Marine Environment & Safety
• /
• v.20 no.6
• /
• pp.768-773
• /
• 2014

In this study, experimental and numerical studies for the synthesis of carbon nanotube(CNT) in methane counterflow diffusion flame have been performed. Methane mixed with acetylene($C_2H_2$) was used as a fuel gas and ferrocene was used as a catalyst for synthesis of CNT. The major parameters was $C_2H_2$ mixing rate and mixing rates were 2 %, 6 %, and 10 %. Characteristics of CNT formation on grid were analyzed from SEM images. the chemical reaction mechanism adopted is GRI-MECH 3.0. Numerical results showed that flame temperature and CO mole fraction were increased with increasing acetylene mixing rate. Experimental results showed that the CNT synthesis in 2% acetylene mixture flame better than that of 6% and 10% acetylene mixture flames. It can be considered that 6% and 10% acetylene mixture flames generated the excessive carbon source and then it interrupted the supplement of the carbon source into ferrocene catalyst. It can be found that the supply of appropriate quantity of carbon source can make effect to synthesis of high purity of CNT.

• Journal of Navigation and Port Research
• /
• v.43 no.2
• /
• pp.79-85
• /
• 2019

Climate change is a very vital issue that can be no longer avoided. Korea has been a top-level country Iin dealing with carbon dioxide emissions since 1960. Many studies have been conducted to suppress or eliminate carbon dioxide emissions, which account for a large portion of greenhouse gases. Carbon Capture and Storage (CCS), the most practical method of them, plays a significant role. However, these methods have the disadvantage of the limits of geographical distribution and high possibility of re-emission into the atmosphere. Recently, ocean storage has been studied using Accelerated Weathering of Limestone (AWL), a technique for storing carbon dioxide in the ocean as an alternative to CCS, an underground storage. AWL is a method of converting carbon dioxide into concentrated water in the form of bicarbonate ion and discharging it to the ocean to dilute and store it. It does not cause re-emission to the atmosphere, and the discharged concentrated water increases the alkalinity of the ocean to prevent marine acidification. The objective of this study was to understand the behavior of DIC (Dissolved Inorganic Carbon) including carbon dioxide during the ocean discharge of bicarbonate ion concentrated water in AWL method. This study area was set near Ulleung-do where sufficient water depth and operational efficiency were secured. CORMIX model was used to calculate the material diffusion by submerged discharge using ship.

• Journal of the Korean Magnetics Society
• /
• v.16 no.1
• /
• pp.75-78
• /
• 2006

In case of contacts between semiconductor and metal in semiconductor circuits, they become unstable because of thermal budget. To prevent these problems, we use diffusion barrier that has a good thermal stability between metal and semiconductor. So we consider the diffusion barrier to prevent the increase of contact resistance between the interfaces of metals and semiconductors, and the increase of resistance and the reaction between the interfaces. In this paper we deposited tungsten boron carbon nitride (W-B-C-N) thin film on silicon substrate. The impurities of the $1000\;{\AA}-thick$ W-B-C-N thin films provide stuffing effect for preventing the inter-diffusion between metal thin films $(Cu-2000\;{\AA})$ and silicon during the high temperature $(700\~1000^{\circ}C)$ annealing process.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2008.04a
• /
• pp.501-504
• /
• 2008

A concrete carbonation model has been constructed that takes account of the diffusion of carbon dioxide through a coating and reaction with calcium hydroxide, and this model has been validated by an accelerated carbonation experiment. (1) By using values for the coatings calculated on the basis of a diffusion.permeation theory as input data for the analysis of diffusion.reaction carbonation in an unsteady state, the effect of the coatings in reducing carbonation can be represented with high accuracy. (2) Through a sensitivity analysis of the diffusion.reaction carbonation model and the experimental results, we found that the diffusion coefficient of calcium hydroxide shows a high interrelationship at 1e-12($m^2/s$). The reaction rate constant for carbonation shows a high interrelationship at 5e-5($m^3/mol/s$).

• Journal of Hydrogen and New Energy
• /
• v.34 no.3
• /
• pp.283-291
• /
• 2023

The physical properties were analyzed for four gas diffusion layers, and gas diffusion electrodes (GDEs) for the cathode of high-temperature polymer electrolyte membrane fuel cell were fabricated through bar coating with three binder to carbon (B/C) ratios. Among them, The GDE from JNT30-A6P showed a significant change in secondary pore volume at a B/C ratio of 0.31, which had the largest pore volume among all GDEs. In the polarization curve, JNT30-A6P GDE showed the best membrane electrode assembly (MEA) performance with a peak power density of 384 mW/cm² at a a B/C ratio of 0.31. From the distribution of relaxation time analysis, the peak 1 corresponding to mass transfer resistance of oxygen reduction reaction (ORR) was significantly reduced in the JNT30-A6P GDE. This is the result that when the binder content decreased, the volume of the secondary pore increased, and the mass transfer resistance of ORR decreased, which played an essential role in the MEA performance.

• Carbon letters
• /
• v.11 no.3
• /
• pp.224-234
• /
• 2010

Four activated carbons were produced by two-stage process as followings; semi-carbonization of indigenous biomass waste, i.e. cotton stalks, followed by chemical activation with KOH under various activation temperatures and chemical ratios of KOH to semi-carbonized cotton stalks (CCS). The surface area, total pore volume and average pore diameter were evaluated by $N_2$-adsorption at 77 K. The surface morphology and oxygen functional groups were determined by SEM and FTIR, respectively. Batch equilibrium and kinetic studies were carried out by using a basic dye, methylene blue as a probe molecule to evaluate the adsorption capacity and mechanism over the produced carbons. The obtained activated carbon (CCS-1K800) exhibited highly microporous structure with high surface area of 950 $m^2/g$, total pore volume of 0.423 $cm^3/g$ and average pore diameter of 17.8 ${\AA}$. The isotherm data fitted well to the Langmuir isotherm with monolayer adsorption capacity of 222 mg/g for CCS-1K800. The kinetic data obtained at different concentrations were analyzed using a pseudo-first-order, pseudo-second-order and intraparticle diffusion equations. The pseudo-second-order model fitted better for kinetic removal of MB dye. The results indicate that such laboratory carbons could be employed as low cost alternative to commercial carbons in wastewater treatment.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.20 no.10
• /
• pp.3243-3250
• /
• 1996

Emission characteristics of nitric oxides and carbon monoxide from a porous media combustor has been experiment studied. The relationship between the change of flame shape and emission has also been examined. As the equivalence ratio decreases, the flame shape on the ceramic matrix plate changes from a diffusion flame, R(radiant)-type flame, to B(Blue)-type flame. With large fuel flow rate, R-type flame turns to be two dimensional R-II type flame around the equivalence of 0.7. Carbon monoxide emission increases very rapid with decreasing equivalence ratio. It changes a lot from some 10 ppm to 100-10,000 ppm with the change of flame type from R-I to R-II type. Nitric oxide emission from the premixed burner is less than 25 ppm over all range of fuel flow rate, which is less than 20% of NOx emission from conventional gas burners.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.29 no.12 s.243
• /
• pp.1321-1328
• /
• 2005

The burning characteristics of interacting coal particles in a convective flow are numerically investigated at various Reynolds numbers. The transient combustion of 2-dimensionally arranged particles, both the fixed particle distances of 5 radii to 20 radii horizontally and 4 radii to 24 radii vertically, is studied. The results obtained from the present numerical analysis indicate that the transient flame configuration and retardation of particle temperature augmentation with the horizontal or vertical particle spacing substantially influence devolatilization process and carbon conversion ratio of interacting particles. Volatile release and carbon conversion ratio of the second particle with decreasing horizontal and vertical particle spacing decrease gradually, whereas those of the first particle with decreasing vertical particle spacing increase due to flow acceleration. When the vertical particle spacing is smaller than $6R_0$, volatile release and carbon conversion ratio of the second particle decrease due to reduction of flame penetration depth and interference of oxygen diffusion by the first particle.