• Electrical & Electronic Materials
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• v.9 no.9
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• pp.906-910
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• 1996

Ferroxplana N $i_{2}$Y(B $a_{2}$N $i_{2}$F $e_{12}$ $O_{22}$ ) magnetic particles, which is one of the hexagonal ferrite were synthesized by a coprecipitation method. The coprecipitates were prepared by adding aqueous solution of BaC $I_{2}$ - 2 $H_{2}$O, NiC $I_{2}$ - 6 $H_{2}$O and FeC $I_{3}$ - 6 $H_{2}$O(of which the mole ratio is $Ba^{+2}$ : N $i^{+2}$ : F $e^{3+}$= 1 : 1 : 6) to a mixture of NaOH and N $a_{2}$C $O_{3}$. The shape of Ferroxplana N $i_{2}$Y magnetic particles obtained at 1, 100(.deg. C) was hexagonal plate-like, average particle size and aspect ratio were 2(.mu.m) and 7, respectively.y.

• 연구논문집
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• s.33
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• pp.147-155
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• 2003

In order to fabricate porous materials having an anisotropic thermal conductivity by aligning plate-shaped pores structure, alumina powder (AM-21, mean particle size $4\mum$) and flake crystalline graphite was used. The aligned pore structure was realized using multi-pressing process. Degree of pore orientation increased with the number of pressing and thermal conductivity, parallel to the pressing direction, decreased with the number of pressing. Thermal conductivity decreased significantly to the addition of 30vol% crystalline graphite, however, in the case of 60vol%, thermal conductivity did not decrease significantly due to the breakage of crystalline graphite. An anisotropy of the thermal conductivity increased with the content of crystalline graphite up to 30vol%. Graded pore structure was fabricated by controlling the content and size of crystalline graphite, which provides, possibly, the enhancement in mechanical strength and thermal insulation properties of the insulating bricks.

• Composites Research
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• v.34 no.1
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• pp.63-69
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• 2021

In order to develop an integrated heat dissipating material and gas barrier film for electronics, new polymer was designed and synthesized for preparing composites containing hexagonal boron nitride (hBN) filler. Depending on the size and content of the hBN filler, both thermal conductivity and oxygen transmission rate can be adjusted. The composite achieved a high thermal conductivity of 28.0 W·m-1·K-1 at most and the oxygen transmission rate was decreased by 62% compared to that of the filler free matrix. Effective filler aspect ratios could be estimated by comparing thermal conductivity and oxygen transmission rate with values predicted by theoretical models. Discrepancy on the aspect ratios extracted from thermal conductivity and oxygen transmission rate comparisons was also discussed.

• Korean Journal of Dental Materials
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• v.44 no.3
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• pp.207-216
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• 2017

The effect of cooling rate on precipitation hardening of a Pd-Cu-Ga-Zn metal-ceramic alloy during porcelain firing simulation was investigated and the following results were obtained. When the cooling rate was fast (Stage 0), the hardness of the alloy increased at each firing step and the high hardness value was maintained. When the cooling rate was slow (Stage 3), the hardness was the highest at the first stage of the firing, but the final hardness of the alloy after complete firing was lower. The increase in hardness of the specimens cooled at the cooling rate of Stage 0 after each firing step was caused by precipitation hardening. The decrease in hardness of the specimens cooled at the cooling rate of Stage 3 after each firing step was attributed to the coarsening of the spot-like precipitates formed in the matrix and plate-like precipitates. The matrix and the plate-like precipitates were composed of the $Pd_2(Cu,Ga,Zn)$ phase of CsCl-type, and the particle-like structure was composed of the Pd-rich ${\alpha}$-phase of face-centered cubic structure. Through the porcelain firing process, Cu, Ga, and Zn, which were dissolved in Pd-rich ${\alpha}$ particles, precipitated with Pd, resulting in the phase separation of the Pd-rich ${\alpha}$ particles into the Pd-rich ${\alpha}^{\prime}$ particles and ${\beta}^{\prime}$ precipitates composed of $Pd_2(Cu,Ga,Zn)$. These results suggested that the durability of the final prosthesis made of the Pd-Cu-Ga-Zn alloy can be improved when the cooling rate is fast during porcelain firing simulation.

• Composites Research
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• v.33 no.3
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• pp.153-160
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• 2020

In this paper, hexagonal boron nitride (h-BN) particles were added between the sheets of prepreg, and the effect of on many properties of BN-embedded carbon fiber reinforced plastics was investigated. The amount of BN particles which corresponds with 0 to 15 wt% of total resin weight was used as an additive material. The tensile strength and the inter-laminar shear strength of BN-embedded CFRP samples were improved by maximally 13.6%, and 6.7%, respectively. The tendency changes of thermal, electrical conductivities and the morphology of cross-section of CFRPs were also observed. This study suggests the possibility of controlling the characteristics of carbon fiber-BN-epoxy composites to use for aerospace applications.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.06a
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• pp.327-327
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• 2008

Lead-free $(K_{0.5}Na_{0.5})NbO_3$ 압전 세라믹스는 다양한 광소자로의 응용과 압전 특성, 초전 특성을 이용한 압전 소자로의 응용이 가능한 재료로 보고되고 있다. 그러나 KNN계 압전소재 특성상 판상 형태의 결정립으로 인해 낮은 소결 밀도를 갖게 되고, 그로인해 압전물성의 저하를 초래하는 문제점을 가지고 있다. 따라서, 본연구에서는 다양한 밀링 방법을 적용하여 입자 사이즈를 작게 하고 소성체의 결정립을 구형화 함으로써 저온소결에서의 압전물성을 개선시키고자 한다. $(K_{0.5}Na_{0.5})NbO_3$를 기계적 분쇄법에 의해 입자사이즈에 따라 변화되는 상의 분석과 압전체로서의 특성을 관찰하였다. 결정학적 상분석 및 미세 조직은 XRD, SEM을 이용하여 관찰하였고, Capacitance는 Impedance analyzer(HP4192A)로 측정하였으며, Impedance 주파수 특성은 Network Analyzer로 측정하여 Kp, Kt와 Qm을 측정하였다.

• Korean Journal of Optics and Photonics
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• v.25 no.6
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• pp.311-314
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• 2014

In this paper, we design a helical fin structure for the heat sink for a high-power LED lighting module, and analyze its thermal properties. By means of the helical fin structure, we can obtain about 14% larger surface area for the limited volume and it can decrease the LED chip temperature by about 12%. Because this helical fin heat sink has 15% less total volume than a conventional one, we can also expect to reduce the production cost due to these structural properties.

• Journal of Korean Tunnelling and Underground Space Association
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• v.3 no.1
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• pp.11-19
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• 2001

The purpose of this study is to improve the problems in Umbrella Arch Method, such as the oxidation, the difficulties in installation and cutting of the steel pipe. The applicability of the high strength FRP (Fiber-Reinforced-Plastic) materials composed of glass fiber as a substitute of steel pipe was investigated in this study. The results of this study show that FRP material is better than steel pipe in work performance and the durability of material except for its price. From the numerical analysis with various types of FRP, it was evaluated that the equiangular curve type is more efficient than the flat type developed abroad, and the supporting effect of FRP-grout mixture is similar to that of steel-grout mixture in results of bending strength test.

• Journal of Biomedical Engineering Research
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• v.20 no.6
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• pp.539-546
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• 1999

현재 상용화되고 있는 치과용 76.5% Pd-11.2% Cu-7.2% GarP 합금의 왁스모형을 원심주조기로 주조하여, 임상조건의 탈개스 및 세라믹 소성처리를 하였다. 이에따른 각각의 시편에 대해 미세조직의 변화를 주사전자현미경 및 EDS로 관찰하고, 최종적인 투과전자현미경으로 조사하였다. 각 조건의 편석, 결정립계 및 석출물부위를 주사전자현미경과 EDS 고 관찰한 결과, 이원계 Pd-GA합금의 안정상들에 해당하는 정량적인 조성비는, 단지 상대적으로 Ga의 성분비만 높게 감지되었다. 특히, 세라믹소성 처리후 미세조직에서 형성된 석출물에 근접한 기지조직일수록 Ga의 농도가 상대적으로 줄어든 고갈현상을 확인하엿다. 또한 투과전자현미경의 제한시야회절도형 분석결과, 주조 및 탈개스처리 후 미세조직의 편석부위에서는 GA의 가장 큰 강도를 보였고, 또 Ga과 Pd 고용체 사이에 미세한 판상의 석출물에 기인하는 줄무늬를 관찰하였다. 한편, 세라믹소성처리후 미세조직의 석출물은 금속간화합물 Pd2Ga으로 밝혀졌으며, 기지조직은 <100> 방향을 따라 약 25nm의 폭을 가지는 미세한 섬유상 형태의 소위 "tweed 조직'을 형성하였다.성하였다.

• Journal of the Korean Wood Science and Technology
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• v.17 no.4
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• pp.77-82
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• 1989

In this study the oxygen index method was used to compare the duration of flaming and the rate of weight loss at the level of 6 and 9mm panel thicknesses among solid wood, plywood, particleboard, and medium density fiberboard. The obtained results were as follows: 1. In 9mm-thick panels, the combustibility was the largest in lauan solid wood followed by medium density fiberboard. particleboard. and plywood. 2. Medium density fiberboard was burned more easily than plywood in 6mm-thick panels and the higher oxygen concentration was needed as the panel thickness increased. 3. The oxygen indices of 9mm-thick panels were 29.0 in lauan solid wood, 31.4 in medium density fiberboard, 33.0 in particleboard, and 33.4 in plywood and those of 6mm-thick panels were 28.3 in medium density fiberboard and 29.7 in plywood. 4. The rate of weight loss was the largest in lauan solid wood followed by medium density fiberboard, plywood, and particleboard.