• Solar Energy
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• v.13 no.2_3
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• pp.65-78
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• 1993

An overdose of fossil fuel for greenhouse heating causes not only the high cost and low quality of agricultural products, but also the environmental pollution of farm village. To solve these problems it is desirable to maximize the solar energy utilization for the heating of greenhouse in winter season. In this study phase change materials were selected to store solar energy concentratively for heating the greenhouse and their characteristics of thermal energy storage were analyzed. The results were summarized as follows. The organic $C_{28}H_{58}$, and the inorganic $CH_3COONa{\cdot}3H_2O\;and\;Na_2SO_4{\cdot}10H_2O$ were selected as low temperature latent heat storage materials. The equation of critical radius was derived to define the generating mechanism of the maximum latent heat of phase change materials. The melting point of $C_{28}H_{58}$ was $62^{\circ}C$, and the latent heat was $50.0{\sim}52.0kcal/kg$. The specific heat of liquid and solid phase was $0.54{\sim}0.69kcal/kg^{\circ}C$ and $0.57{\sim}0.75kcal/kg^{\circ}C$ respectively. The melting point of $CH_3COONa{\cdot}3H_2O$ was $61{\sim}62^{\circ}C$, the latent heat was $64.9{\sim}65.8$ kcal/kg and the specific heat of liquid and solid phase was respectively $0.83kcal/kg^{\circ}C$ and $0.51{\sim}0.52kcal/kg^{\circ}C$. The melting point of $Na_2SO_4{\cdot}10H_2O$ was $30{\sim}30.9^{\circ}C$, the latent heat was 53.0 kcal/kg and the specific heat of liquid and solid phase was respectively $0.78{\sim}0.89kcal/kg^{\circ}C$ and $0.50{\sim}0.7kcal/kg^{\circ}C$ When the urea of 21.85% was added to control the melting point of $Na_2SO_4{\cdot}10H_2O$ and the phase change cycles were repeated from 0 to 600, the melting point was $16.7{\sim}16.0^{\circ}C$ and the latent heat was $36.0{\sim}28.0kcal/kg^{\circ}C$.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.3
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• pp.576-583
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• 2018

Silicon carbide is considered to be a potentially useful material for high-temperature electronic devices, as its band gap is larger than that of silicon and the p-type and/or n-type conduction can be controlled by impurity doping. Particularly, porous n-type SiC ceramics fabricated from ${\beta}-SiC$ powder have been found to show a high thermoelectric conversion efficiency in the temperature region of $800^{\circ}C$ to $1000^{\circ}C$. For the application of SiC thermoelectric semiconductors, their figure of merit is an essential parameter, and high temperature (above $800^{\circ}C$) electrodes constitute an essential element. Generally, ceramics are not wetted by most conventional braze metals,. but alloying them with reactive additives can change their interfacial chemistries and promote both wetting and bonding. If a liquid is to wet a solid surface, the energy of the liquid-solid interface must be less than that of the solid, in which case there will be a driving force for the liquid to spread over the solid surface and to enter the capillary gaps. Consequently, using Ag with a relatively low melting point, the junction of the porous SiC semiconductor-Ag and/or its alloy-SiC and/or alumina substrate was studied. Ag-20Ti-20Cu filler metal showed promise as the high temperature electrode for SiC semiconductors.

• Korean Journal of Food Science and Technology
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• v.31 no.1
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• pp.24-29
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• 1999

The physicochemical properties of tagatose, a low calorie sweetener, was investigated. Rheological property of tagatose solution was found to be Bingham fluid. As the concentration of tagatose increased from 10 to 50% at $25^{\circ}C$, the viscosity increased from 1.65 to 5.14 cp. When the temperature of 40% tagatose solution increased from 15 to $55^{\circ}C$, the viscosity decreased from 4.59 to 2.33cp. The melting onset temperature and endothermic enthalpy of tagatose were $130.4^{\circ}C$ and -202.3 J/g, respectively, which were obtained from the analysis of differential scanning calorimetry. Tagatose showed higher water absorption than sucrose under $85{\sim}100%$ of relative humidity. Tagatose was less soluble than sucrose at $20{\sim}70^{\circ}C$. Water activity of tagatose in 60% concentration was 0.892, which was lower than 0.957 of sucrose solution. Tagatose solution adjusted from pH 2 to pH 12 was stable after 3 days. Amount of tagatose was not changed after heat treatment at $154^{\circ}C$ for 4 hours. But a browning reaction was found and absorbance of a tagatose solution increased with heat treatment.

• Journal of the Microelectronics and Packaging Society
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• v.21 no.4
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• pp.97-103
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• 2014

Among various lead-free solders, the Sn-58Bi solders have been considered as a highly promising lead-free solders because of its low melting temperature and high tensile strength. However, Sn-58Bi solder has the poor ductility. To enhance the mechanical property of Sn-58Bi solder, epoxy-enhanced Sn-58Bi solders have been studied. This study compared the microstructures and the mechanical properties of Sn-58Bi solder and Sn-58Bi epoxy solder with aging treatment. The solders ball were formed on the printed circuit board (PCB) with organic solderability preservative (OSP) surface finish, and then the joints were aged at 85, 95, 105 and $115^{\circ}C$ for up to 100, 300, 500 and 1000 hours. The shear test was conducted to evaluate the mechanical property of the solder joints. $Cu_6Sn_5$ intermetallic compound (IMC) layer grew with increasing aging time and temperature. The IMC layer for the Sn-58Bi epoxy solder was thicker than that for the Sn-58Bi solder. According to result of shear test, the shear strength of Sn-58Bi epoxy solder was higher than that of Sn-58Bi solder and the shear strength decreased with increasing aging time.

• Applied Chemistry for Engineering
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• v.4 no.3
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• pp.601-615
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• 1993

A series of polycarbonate(PC)/polyamide 6(PA6) blends were prepared by three different blending methods to investigate their compatibility. From the DSC results, all of these blends have two Tg's in their own Tg regions, and there was no significant depression of the melting point and the crystallization temperature of PA6. With respect to the microstructure of the blends by SEM, the phase separation occurred at very low blend compositions, PC/PA6=95/5 and 5/95, already. In addition, a method is proposed to determine the Flory-Huggins polymer-polymer interaction parameter(${\chi}_{12}$) in polymer blend systems by using the experimentally determined Tg's. The values of ${\chi}_{12}$ obtained were 0.0381, 0.0411, 0.0418, for solution casting, solution precipitation, and extrusion blending methods, respectively. These values were higher than the critical value of ${\chi}_{12}$,($({\chi}_{12})_c$, 0.0271). Therefore it was concluded that the PC/PA6 blend system have little compatibility.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.11
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• pp.1135-1140
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• 2012

Two-step metallization processes have been proposed to achieve high-efficiency silicon solar cells, where the front-side grids are formed by silver plating after the formation of a nickel seed layer with a mask. Because the conventional mask patterning process is performed by an expensive selective printing method using either UV resist or phase change ink, however, the combination of a simple coating and laser-selective ablation processes is proposed in this study as an alternative means. As a masking material, the solar cell wafer was coated with either inexpensive wax having a low melting temperature or a fluorocarbon solution, and then, an electrode image was patterned by selectively removing the masking material using the laser. It was found that the fluorocarbon coating was not only superior to the wax coating in terms of pattern uniformity but it also increased the efficiency of the solar cell by 0.16%, as confirmed by statistical f and t tests.

• Polymer(Korea)
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• v.24 no.4
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• pp.513-519
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• 2000

The effect of petroleum resin as a tackifier for polyalphaolefin (APAO) hot melt adhesive on thermal properties, crystallinity and adhesion strength was investigated. The presence of petroleum resin resulted in the melting temperature decrease in APAO/petroleum blend, especially, in APAO with low ethylene content/C$_{5}$ petroleum blend. It was also found that petroleum resin caused the decrease of crystallinity regardless of ethylene content in APAO. The maximum adhesion strength was found to be at 50/50 (APAO/petroleum) composition. $C_{5}$ resin was more effective to increase adhesion strength than $C_{9}$ for APAO with high ethylene content. In addition, it was found that the adhesion strength was improved with the decrease of crystallinity in APAO/petroleum resin hot melts.

• Polymer(Korea)
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• v.24 no.2
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• pp.281-286
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• 2000

A series of amorphous polyesters were synthesized from amorphous polyether and sebacoyl chloride. The structure and competition of the obtained aliphatic polyester were confirmed by $^1$H-NMR and FT-IR. The number average molecular weights (M$_{n}$) of the obtained polymer were ranging from 8000 ~ 15000. These polyesters showed no crystallinity and their glass transition temperatures (T$_{g}$) were around -77$^{\circ}C$. For comparison, aliphatic polyesters were also synthesized from poly(ethylene glycol) (PEG) with M$_{n}$ of 200, 400, and 1000. As the M$_{n}$ of PEG increased, the melting point of the obtained polyester increased, and the crystallinity of the obtained polyester increased showing 8.8%, 16.2%, and 46.7%, respectively.ively.y.

• Journal of the Korea Institute of Building Construction
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• v.16 no.1
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• pp.25-34
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• 2016

From 1990's, a study on the development of exothermic concrete, a concrete which electro-conductive material is mixed, has been proceeded. However, due to the difficulty of exothermic reproducibility of concrete specimen, the study has been unable to continuously carried out. Accordingly, this study was focused on developing an exothermic concrete for the purpose of snow-melting material. Cement paste and mortar specimens mixed with graphite, conductive metal powder and chemical admixture were made. The evaluation of exothermic performance and reproducibility was conducted under $-2^{\circ}C$ of low temperature. In addition, micro-chemical analysis was carried out to investigate a cause of exothermic reproducibility. As a test result, the specimen mixed with graphite and superplasticizer with air entrained showed the best exothermic performance and reproducibility. Through micro-chemical analysis, it is judged that polymer or methacrylic acid (MAA), the contents inside the superplasticizer with air entrained, gave exothermic reproducibility by generating the electrochemical reaction with graphite.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2004.05a
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• pp.173-176
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• 2004

In this study we investigated post ELA(Excimer Laser Annealing) effect on SMC (Silicide Mediated Crystalization) poly-Si (Polycrystalline Silicon) to improve the characteristics of poly-Si. Combining SMC and XeCl ELA were used to crystallize the a-Si (amorphous Silicon) at various ELA energy density for LTPS (Low Temperature Polycrystalline Silicon). We fabricated the conventional SMC poly-Si with no SPC (Solid Phase Crystallization) phase using UV heating method[1] and irradiated excimer laser on SMC poly-Si, so called SMC-ELA poly-Si. After using post ELA we can get better surface morphology than conventional ELA poly-Si and enhance characteristics of SMC poly-Si. We also observed the threshold energy density regime in SMC-ELA poly-Si like conventional ELA poly-Si.