• Journal of the Korean Ceramic Society
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• v.40 no.3
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• pp.234-240
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• 2003

Hardened cement pastes of OPC which contains 10 wt% CSA type expansive additives were immersed in aqueous solution of 10 wt% MgS $O_4$.7$H_2O$ and then investigated by compressive strength, XRD. SEM and DSC etc.. According to the results including the hydration products and the microstructure of the hardened paste, the case of CSA type expansive additives［No. 6(C/(equation omitted) : 2.29, A/(equation omitted) : 0.16)] prepared from raw materials increased the resistance to $Mg^{2＋}$, S $O_4$$^{2-}$ ion diffusion than that of OPC paste due to the densification by the formation of fine ettringite in the first stage and the hydrates according to $\beta$-C$_2$S hydration in the late period.

• Transactions on Electrical and Electronic Materials
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• v.6 no.2
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• pp.78-84
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• 2005

Standard crystalline solar cells are generally fabricated with the front grid pattern of silver paste contact. We have reported a detailed theoretical analysis of the proposed segmented cross grid line pattern in this paper. This work was carried out for the optimization of spacing and width of grid finger, main busbar and sub-busbar. The overall electrical and optical losses due to front contact were brought down to $10\%$ or even less as compared to the usual loss of $15\%$ or more in the conventional screen printed silver paste technology by choosing proper grid pattern and optimizing the grid parameters. The total normalized power loss for segmented mesh grid with plated metal contact was also observed and the total power loss could be brought down to $10.04\%$ unlike $11.57\%$ in the case of continuous grid and plated contact. This paper is able to outline the limitations of conventional screen printed contact.

• Advances in concrete construction
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• v.11 no.3
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• pp.183-192
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• 2021

Due to economic and environmental benefits, increasing the substitution ratio of ordinary cement by industry by-products like fly ash (FA) is one of the best approaches to reduce the impact of the concrete industry on the environment. However, as the substitution rate of FA increases, it will have an adverse impact on the performance of cement-based materials, so the actual substitution rate of FA is limited to around 10-30%. Therefore, in order to increase the early-age strength of high replacement (30-70%) low-calcium ultrafine FA blended cement paste, sodium sulfate and calcium sulfate dihydrate were used to improve the reactivity of FA. The results show that sodium sulfate has a significant enhancement effect on the strength of the composite pastes in the early and late ages, while calcium sulfate dihydrate has only a slight effect in the late ages. The addition of sodium sulfate in the cement-FA blended system can enhance the gain rate of non-evaporation water, and can decrease the Ca(OH)2 content. In addition, when the sulfate chemical activators are added, the ettringite content increases, and the surface of the FA is dissolved and hydrated.

• Korean Journal of Materials Research
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• v.22 no.2
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• pp.103-109
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• 2012

Red-emitting $Eu^{3+}$-activated $(Y_{0.95-x}Al_x)VO_4$ (0 < x $\leq$ 0.12) nanophosphors with the particle size of ~30 nm and the high crystallinity have been successfully synthesized by a hydrothermal reaction. In the synthetic process, deionized water as a solvent and ethylene glycol as a capping agent were used. The crystalline phase, particle morphology, and the photoluminescence properties of the excitation spectrum, emission intensity, color coordinates and decay time, of the prepared $(Y_{0.95-x}Al_x)VO_4:Eu^{3+}$ nanophosphors were compared with those of the $YVO_4:Eu^{3+}$. Under 147 nm excitation, $(Y_{0.95-x}Al_x)VO_4$ nanophosphors showed strong red luminescence due to the $^5D_0-^7F_2$ transition of $Eu^{3+}$ at 619 nm. The luminescence intensity of $YVO_4:Eu^{3+}$ enhanced with partial substitution of $Al^{3+}$ for $Y^{3+}$ and the maximum emission intensity was accomplished at the $Al^{3+}$ content of 10 mol%. By the addition of $Al^{3+}$, decay time of the $(Y,Al)VO_4:Eu^{3+}$ nanophosphor was decreased in comparison with that of the $YVO_4:Eu^{3+}$ nanophosphor. Also, the substitution of $Al^{3+}$ for $Y^{3+}$ invited the improvement of color coordinates due to the increase of R/O ratio in emission intensity. For the formation of transparent layer, the red nanophosphors were fabricated to the paste with ethyl celluloses, anhydrous terpineol, ethanol and deionized water. By screen printing method, a transparent red phosphor layer was formed onto a glass substrate from the paste. The transparent red phosphor layer exhibited the red emission at 619 nm under 147 nm excitation and the transmittance of ~80% at 600 nm.

• Journal of the Korean Ceramic Society
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• v.40 no.8
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• pp.804-810
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• 2003

The fine powder produced by heating and grinding of the waste concrete in the waste construction was investigated whether utilize as substitution raw material of SiO$_2$, CaO, and Al$_2$O$_3$ source for OPC clinker manufacture is possible or not. In order to synthesize OPC clinker, limestone, shale, converter slag and fly ash were used as main raw materials, and modulus was fixed LSF 91.0, SM 2.60, IM 1.60. The synthesized clinkers were characterized. The Main products of synthesized clinker were C$_3$S, ${\beta}$-C$_2$S, C$_3$A, C$_4$AF as OPC clinker at 1,43$^{\circ}C$. As a result of TG-DTA and burnability index(B.U) analysis of each raw mixtures, the formation temperature of clinker phases was similar and B.I was showed easy burning as 48.6∼51.4.

• Journal of the Korean Recycled Construction Resources Institute
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• v.5 no.4
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• pp.353-358
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• 2017

The aim of this research is providing a fundamental idea on reducing viscosity of high performance cementitous materials. In rheological aspect, to determine the fluidity of the cementitious materials, both yield stress and viscosity should be controlled. For the high performance cementitious materials with low water-to-binder ratio and high volume fraction, it was difficult to reduce the viscosity with superplasticizer while reducing yield stress was relatively easy. Hence, in this research, with the goal of reducing viscosity of the cementitious materials, both ways of reducing viscosity were suggested: achieving proper combination of powder conditions, and adding low-viscosity typed water reducer. First, by replacing various byproduct powders, specifically, raw coal ash and wasted limestone powder showed favorable results on reducing viscosity of the cement paste. Regarding the low viscosity typed superplasticizer, it showed a good performance on reducing viscosity comparing with generic superplasticizer. Therefore, based on the results of this research, it is expected to provide a fundamental idea on reducing viscosity of cementitious materials by various methods.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.36 no.5
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• pp.339-346
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• 2023

The uncertainties of microstructural features affect the properties of materials. Numerous pores that are randomly distributed in materials make it difficult to predict the properties of the materials. The distribution of pores in cementitious materials has a great influence on their mechanical properties. Existing studies focus on analyzing the statistical relationship between pore distribution and material responses, and the correlation between them is not yet fully determined. In this study, the mechanical response of cementitious materials is predicted through an image-based data approach using a convolutional neural network (CNN), and the correlation between pore distribution and material response is analyzed. The dataset for machine learning consists of high-resolution micro-CT images and the properties (tensile strength) of cementitious materials. The microstructures are characterized, and the mechanical properties are evaluated through 2D direct tension simulations using the phase-field fracture model. The attributes of input images are analyzed to identify the spot with the greatest influence on the prediction of material response through CNN. The correlation between pore distribution characteristics and material response is analyzed by comparing the active regions during the CNN process and the pore distribution.

• Journal of the Korean Society of Food Culture
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• v.17 no.1
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• pp.78-89
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• 2002

Preferences of 814 elderly living in Incheon for dishes, food materials and cooking methods were investigated. The survey was conducted from Dec. 2000 to Jan. 2001 by questionnaires. Subjects preferred cooked rice with beans, kalkooksoo(hot noodle), gomtang(soup with beef), bibimbap(rice with assorted mixture) to other staple dishes. However, preference for hashed rice or curried rice was very low. More than 50% of the subjects liked soybean paste soup and stew, and the ratio of elderly who liked Chinese cabbage kimchi was 68.7%. There was no significant difference in preference for pan-fried foods according to food materials in them. Subjects liked injolmi(waxy rice cake), shikhye(fermented rice drink) and coffee the most. Most subjects preferred plant foods like vegetables, legumes and seaweeds to animal foods. Preference of elderly for milk and yoghurt was reatively high; however, that for ham, butter and cheese was low. Elderly in Incheon liked roasted beef, beef soup and roasted pork the most. Chicken was preferred when it was boiled in water with garlic, ginseng, and so on. Cooked and seasoned vegetables (Namul) were the most preferred type by elderly. Preferences for dishes and food materials were more affected by living places of the subjects than by sex, and the reverse was true in preference for cooking method of food materials.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.33 no.5
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• pp.367-372
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• 2020

As packaging processes for atomic gyroscope vapor cells, the glass tube tip-off process, anodic bonding, and paste sealing have been widely studied. However, there are stability issues in the alkali metal which are caused by impurity elements and leakage during high-temperature processes. In this study, we investigated the applicability of a vapor cell low-temperature packaging process by depositing Au on a Pyrex cell in addition to forming an Au-Sn thin film on a cap to cover the cell, followed by laser irradiation of the Au/Au-Sn interface. The mechanism of the thin film bonding was evaluated by XRD, while the packaging reliability of an Ne gas-filled vapor cell was characterized by variation of plasma discharge behavior with time. Furthermore, we confirmed that the Rb alkaline metal inside the vapor cell showed no color change, indicating no oxidation occurred during the process.

• Korean Journal of Materials Research
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• v.14 no.11
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• pp.807-812
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• 2004

The uniformity of emission mage and field emission properties of carbon nanotube(CNT) cathodes dependence on CNT particle dispersion were investigated for field emission displays. We used multi-walled carbon nanotubes (MWNTs) synthesized by CVD method as the field emitter materials. CNT dispersion in CNT ink was carried out by ultrasonication and shaking methods. According to CNT dispersion conditions, the uniformity of emission image and field emission properties of CNT cathodes were greatly affected. The smaller particles of filler materials and CNT powders provide the better properties of the CNT cathodes.