• 한국세라믹학회지
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• 제30권5호
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• pp.347-356
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• 1993

In joining alumina ceramics to metal by using Mo-Mn metallizing process the effects of metallizing thickness, temperature, and the composition of paste on the bond strength and the microstructure of joining interface were investigated. The bond strength variation in the range of metallizing temperature, 1350~155$0^{\circ}C$ was more than 150MPa above 145$0^{\circ}C$ and the optimum metallizing thickness was 30${\mu}{\textrm}{m}$. The optimum contents of Mn in Mo-Mn paste was 5% due to the bond strength decrease with the increase of addition. The effect of SiO2 addition in paste on bond strength was saturated around 200MPa. It was also observed that as the particle size of Mo decreased, the joinning with higher bond strength was shown in spite of low metallizing temperature.

• Computers and Concrete
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• 제32권6호
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• pp.567-576
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• 2023

In this study, a 3D microstructure-based model is established to simulate the effective thermal conductivity of cement paste, covering varying influencing factors associated with microstructure and thermal transfer mechanisms. The virtual cement paste divided into colloidal C-S-H and heterogeneous paste are reconstructed based on its structural attributes. Using the two-level hierarchical cement pastes as inputs, a lattice Boltzmann model for heat conduction is presented to predict the thermal conductivity. The results suggest that due to the Knudsen effect induced by the nanoscale pore, the thermal conductivity of air in C-S-H gel pore is significantly decreased, maximumly accounting for 3.3% thermal conductivity of air at the macroscale. In the cement paste, the thermal conductivities of dried and saturated cement pastes are stable at the curing age larger than 100 h. The high water-to-cement ratio can decrease the thermal conductivity of cement paste.

• 한국수산과학회지
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• 제21권5호
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• pp.277-287
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• 1988

In this paper, the influence of heating medium on the thermal diffusivities of fish meat paste products was studied. Model products were heated in boiling water, saturated steam and soybean oil. The differences in temperature raise of the products were interpreted with Biot number of the products. Because of the large overall heat transfer coefficient of heating medium, the temperature raise of the products in boiling water and saturated steam was fast and the Biot number of the products could be recognized as infinite. But the temperature raise of the products in soybean oil was slow and the Biot number of the products was less than 50.

• 전기학회논문지
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• 제61권6호
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• pp.916-921
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• 2012

Sealant paste with silica immersed in cross-linked epoxy-acrylate polymer resin was prepared by thermal and UV curing process. The curing mechanism of polymer resin resulted from 2 functional groups of epoxy and acrylic structure. The properties of microstructure, thermal conductivity and mechanical strength were investigated for its various applications. The adhesion strength is increased by increasing the thermal curing time until 15 minutes, and curing efficiency is saturated over 20 minutes. The increase rate per day of pot life and viscosity is 4.8%, indicating it has excellent storage stability. It is found that the formulation of silica pastes can be applied to heavy industries, building materials, display and various industries.

• Computers and Concrete
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• 제23권2호
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• pp.145-153
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• 2019

Adaptive schemes are constructed in this paper for modeling the effective chloride diffusion coefficient of cement-based materials (paste and concrete). Based on the polarization approximations for the effective conductivity of isotropic multicomponent materials, we develop some fitting procedures to include more information about the materials, to improve the accuracy of the scheme. The variable reference parameter of the approximation involves a few free scalars, which are determined through the available numerical or experimental values of the macroscopic chloride diffusion coefficient of cement paste or concrete at some volume proportions of the component materials. The various factors that affect the chloride diffusivity of cement-based material (porous material structure, uncertainty of value of the chloride diffusion coefficient in water-saturated pore spaces, etc.) may be accounted to make the predictions more accurate. Illustrations of applications are provided in a number of examples to show the usefulness of the approach.

• Computers and Concrete
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• 제4권4호
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• pp.273-284
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• 2007

The paper considers a theoretical model for the study of the process of transfer of sulfate ions in saturated porous media - mineral composites. In its turn, the model treats diffusion of sulfate ions into cement based composites, accounting for simultaneous effects such as filling of micro-capillaries with ions and chemical products and liquid push out of them. The proposed numerical algorithm enables one to account for those simultaneous effects, as well as to model the diffusive behavior of separate sections of the considered volume, such as inert fillers. The cases studied illustrate the capabilities of the proposed model and those of the algorithm developed to study diffusion, considering the specimen complex configuration. Computations show that the theoretical assumptions enable one to qualitatively estimate the experimental evidence and the capabilities of the studied composite. The results found can be used to both assess the sulfate corrosion in saturated systems and predict and estimate damage of structures built of cement-based mineral composites.

• Computers and Concrete
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• 제4권2호
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• pp.157-166
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• 2007

The paper considers a theoretical model to study sulfate ion diffusion in saturated porous media - cement based mineral composites, accounting for simultaneous effects, such as filling micro-capillaries (pores) with ions and chemical products and liquid push out of them. Pore volume change and its effect on the distribution of ion concentration within the specimen are investigated. Relations for the distribution of the capillary relative radius and volume within the composite under consideration are found. The numerical algorithm used is further completed to consider capillary size change and the effects accompanying sulfate ion diffusion. Ion distribution within the cross section and volume of specimens fabricated from mineral composites is numerically studied, accounting for the change of material capillary size and volume. Characteristic cases of 2D and 3D diffusion are analyzed. The results found can be used to both assess the sulfate corrosion in saturated systems and predict changes occurring in the pore structure of the composite as a result of sulfate ion diffusion.

• 한국환경농학회지
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• 제38권2호
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• pp.69-75
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• 2019

BACKGROUND: Measurement of electrical conductivity of saturated soil paste ($EC_e$) for assessment of soil salinity is time-consuming, and thus conversion of EC of 1:5 soil-water extract ($EC_{1:5}$) to $EC_e$ using a dilution factor may be of help to monitor salinity of huge number of soil samples. This study was conducted to evaluate the dilution factor for reclaimed tideland (RTL) soils of South Korea. METHODS AND RESULTS: Soil samples (n=40) were collected from four RTLs, and analyzed for $EC_{1:5}$, $EC_e$, and cation compositions of 1:5 soil-water extract. The dilution factor (8.70) was estimated by regression analysis between $EC_{1:5}$ and $EC_e$, and the obtained dilution factor was validated by applying to an independent data set (n=96) of $EC_{1:5}$ and $EC_e$. The $EC_e$ measured and predicted was strongly correlated ($r^2=0.74$, P<0.001), but $EC_e$ was overestimated by 16% particularly for the soils with high clay content and low sodium adsorption ratio (SAR). CONCLUSION: This study suggests that using the dilution factor to convert $EC_{1:5}$ to $EC_e$ is feasible method to monitor changes in the soil salinity of the study RTL. However, overestimation of $EC_e$ should be cautioned for the soils with high clay content and low SAR.

• Bulletin of the Korean Chemical Society
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• 제29권5호
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• pp.915-920
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• 2008

In this paper the electrochemical behaviors of hydroquinone ($H_2Q$) were investigated on a carbon paste electrode using room temperature ionic liquid N-butylpyridinium hexafluorophosphate ($BPPF_6$) as binder (ILCPE) and further applied to $H_2Q$ determination. In pH 2.5 phosphate buffer solution (PBS), the electrochemical response of H2Q was greatly improved on the IL-CPE with a pair of well-defined quasi-reversible redox peaks appeared, which was attributed to the electrocatalytic activity of IL-CPE to the $H_2Q$. The redox peak potentials were located at 0.340 V (Epa) and 0.240 V (Epc) (vs. the saturated calomel electrode, SCE), respectively. The formal potential ($E^0$') was calculated as 0.290 V and the peak-to-peak separation (${\Delta}E_p$) was 0.100 V. The electrochemical parameters of $H_2Q$ on the IL-CPE were further calculated by cyclic voltammetry. Under the selected conditions the anodic peak current was linear with $H_2Q$ concentration over the range from $5.0\;{{\times}}\;10^{-6}$ to $5.0\;{\times}\;10^{-3}\;mol\;L^{-1}$ with the detection limit as $2.5\;{\times}\;10^{-6}\;mol\;L^{-1}$ (3$\sigma$ ) by cyclic voltammetry. The proposed method was successful applied to determination of $H_2Q$ content in a synthetic wastewater sample without the interferences of commonly coexisting substances.

• 한국건설순환자원학회논문집
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• 제6권1호
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• pp.95-102
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• 2011

순환굵은골재 콘크리트에서 혼합전의 순환굵은골재에 부착되어 있었던 모르타르의 성상변화를 조사하기 위한 방법으로, 시멘트풀 속에 순환굵은골재를 투입하여 경화시킨 다음 순환굵은골재에 부착된 모르타르의 비캇경도와 공극분포를 검토하였다. 이때 순환굵은골재는 모재콘크리트의 압축강도를 3수준(25.5MPa, 41.7MPa, 60.1MPa)으로 변화시켜 제조한 것을 파쇄시킨 다음 표면건조포화상태 및 절대건조상태에서 사용되었다. 실험결과 순환굵은골재에 부착된 모르타르의 비캇경도는 순환굵은골재의 모재콘크리트의 강도가 클수록 크며, 재령이 증가할수록 크게 되는 것으로 나타났다. 또한, 시멘트풀 속에서 부착모르타르의 공극분포는 $100nm{\sim}10{\mu}m$ 크기의 공극이 감소되며, 6nm~100nm 크기의 작은 공극이 증가하는 것으로 나타났다.