• 한국결정성장학회지
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• 제17권3호
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• pp.128-132
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• 2007

방전플라즈마 소결법을 적용하여 탄화붕소 세라믹스를 제조하여 그 소결 특성, 미세 구조 및 기계적 특성을 평가하였다. 탄화붕소의 소결에 방전플라즈마 소결법을 적용하여 소결 조제의 첨가 없이 전통적인 소결법보다 낮은 온도에서 99% 이상의 완전 치밀화된 소결체를 제작할 수 있었으며, 탄화붕소 분말의 메탄을 세척을 통하여 분말 표면에 형성되어 있는 $B_2O_3$ 상을 사전에 제거함으로써 결정립의 조대화를 방지하여 균일한 미세구조의 형성을 유도할 수 있었으며 결과적으로 탄화붕소 소결체의 기계적 특성을 향상시킬 수 있었다. 특히 파괴인성의 경우 메탄을 세척을 통하여 30% 이상의 물성 향상을 달성하였다.

• Journal of Magnetics
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• 제18권4호
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• pp.400-404
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• 2013

Grain boundary diffusion technique with $DyH_3$ nanoparticles was applied to fabricate Dy-less sintered Nd-Fe-B permanent magnets with high coercivity. The magnetic properties and microstructure of magnets were systematically studied. The coercivity and remanence of grain boundary diffusion magnet were improved by 60% and reduced by 7% compared with those of the original magnet, respectively. Meanwhile, both the remanence temperature coefficient (${\alpha}$) and the coercivity temperature coefficient (${\beta}$) of the magnets were improved after diffusion treatment. Investigation shows that Dy is preferentially enriched as (Nd, Dy)$_2Fe_{14}B$ phase in the surface region of the $Nd_2Fe_{14}B$ matrix grains indicated by the remarkable enhancement of the magneto-crystalline anisotropy field of the magnet. As a result, the magnet diffused with a small amount of Dy nanoparticles possesses enhanced coercivity without remarkably sacrificing its magnetization.

• 한국세라믹학회지
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• 제52권6호
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• pp.441-448
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• 2015

Silicon carbide (SiC) coatings for tri-isotropic (TRISO) nuclear fuel particles were fabricated using a chemical vapor deposition (CVD) process onto graphite. A micro-tensile-testing system was developed for the mechanical characterization of SiC coatings at high temperatures. The fracture strength of the SiC coatings was characterized by the developed micro-tensile test in the range of $25^{\circ}C$ to $1000^{\circ}C$. Two types of CVD-SiC films were prepared for the micro-tensile test. SiC-A exhibited a large grain size (0.4 ~ 0.6 m) and the [111] preferred orientation, while SiC-B had a small grain size (0.2 ~ 0.3 mm) and the [220] preferred orientation. Free silicon (Si) was co-deposited onto SiC-B, and stacking faults also existed in the SiC-B structure. The fracture strengths of the CVD-SiC coatings, as measured by the high-temperature micro-tensile test, decreased with the testing temperature. The high-temperature fracture strengths of CVD-SiC coatings were related to the microstructure and defects of the CVD-SiC coatings.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2000년도 하계학술대회 논문집
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• pp.802-805
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• 2000

Anistropic [Ta/NdFeB/Ta] thin film was sputtered on heated Si substrate by Nd$\_$17/Fe$\_$74/B$\_$9/ target. The grain size of the films increased according to the increase of substrate temperature, and the film deposited at 650$^{\circ}C$ showed optimum coercivity. 4$\pi$M$\_$r/, $\_$i/H$\_$c/ and (BH)$\_$max/ measured perpendicular to the film plane of thin film deposited at 650$^{\circ}C$ are 12.3 kG, 9.9 kOe and 37 MGOe, respectivly.

• 한국정밀공학회지
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• 제29권3호
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• pp.273-278
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• 2012

$ZrB_2$ has a melting temperature of $3245^{\circ}C$ and a low density of $6.1\;g/cm^3$, which makes this a candidate for application to ultra-high temperature over $2000^{\circ}C$. Beside these properties, $ZrB_2$ has excellent resistance to thermal shock and oxidation compared with other non-oxide engineering ceramics. This paper reviewed briefly 2 research examples, which are related to densification and properties of $ZrB_2$-based ceramics for ultra-high temperature applications. In the first section, the effect of $B_4C$ addition on the densification and properties of $ZrB_2$-based ceramics is shown. $ZrB_2$-20 vol.% SiC system was selected as a basic composition and $B_4C$ or C was added to this system in some extents. With sintered bodies, densification behavior and hightemperature (up to $1400^{\circ}C$) properties such as bending strength and hardness are examined. In the second section, the effect of the SiC size on the microstructures and physical properties is shown. $ZrB_2$-SiC ceramics are fabricated by using various SiC sources in order to investigate the grain-growth inhibition and the mechanical/thermal properties of $ZrB_2$-SiC.

• 한국자기학회지
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• 제7권5호
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• pp.250-257
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• 1997

Ar+N$_{2}$ 가스분위기에서 반응성 스퍼터링법으로 제조된 Fe-Nb-B-N 박막의 미세구조 및 자기적 특성을 조사하였다. 질소첨가한 적정조성의 Fe-Nb-B-N 박막은 우수한 고주파 연자기 특성을 보였는데, 그 특성은 다음과 같다. 포화자화(4 .pi. M$_{s}$ )는 16.5 kG, 보자력(H$_{c}$)은 0.13 Oe, 1 MHz에서의 실효투자율은 약 5,000의 값을 나타내었다. 특히 실효투자율은 10 MHz까지 겨의 변화가 없었으며, 100 MHz에서도 약 2,000의 값을 보여 매우 우수한 고주파 특성을 가진 재료로 판단된다. 한편, 이러한 우수한 특성을 지닌 Fe-Nb-B-N 박막의 미세구조를 TEM으로 관찰한 결과, 적정 열처리온도인 590 .deg. C에서 열처리한 Fe-Nb-B-N 박막은 약 5 ~ 10 nm의 .alpha. -Fe phase, Nb-nitride의 석출물과 Nb-B rich 비정질상 등으로 이루어져 있음을 알 수 있었다. 반면에 N이 첨가되지 않은 Fe-Nb-B 박막의 경우에는 약 10 nm정도의 .alpha. -Fe결정립과 Nb-B rich 비정질상의 두가지 상으로 이루어져 있다. 따라서 N을 첨가한 경우에 더욱 미세한 .alpha. -Fe 결정립을 얻을 수 있음이 확인되었다. 이는 N 첨가로 인한 결정립의 미세화 효과 와 Nb-nitride 형성으로 인한 결정립 성장의 억제효과에 의한 것으로 생각된다. 따라서 Fe-Nb-B-N 박막의 우수한 연자기 특성은 결정립 미세화에 기인하는 것으로 판단된다.

• 한국재료학회지
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• 제14권4호
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• pp.246-250
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• 2004

We have investigated the effects of boron added to Cu film on the Cu-Ti reaction and microstructural evolution of Cu(B) alloy film during annealing of Cu(B)/Ti/$SiO_2$/Si structure. The result were compared with those of Cu(B)/$SiO_2$ structure to identify the effects of Ti glue layers on the Boron behavior and the result grain growth of Cu(B) alloy. The vacuum annealing of Cu(B)/Ti/$SiO_2$ multilayer structure allowed the diffusion of B to the Ti surface and forming $TiB_2$ compounds at the interface. The formed $TiB_2$ can act as a excellent diffusion barrier against Cu-Ti interdiffusion up to $800^{\circ}C$. Also, the resistivity was decreased to $2.3\mu$$\Omega$-cm after annealing at $800^{\circ}C$. In addition, the presence of Ti underlayer promoted the growth Cu(l11)-oriented grains and allowed for normal growth of Cu(B) film. This is in contrast with abnormal growth of randomly oriented Cu grains occurring in Cu(B)/$SiO_2$ upon annealing. The Cu(B)/Ti/$SiO_2$ structure can be implemented as an advanced metallization because it exhibits the low resistivity, high thermal stability and excellent diffusion barrier property.

• 한국응용곤충학회지
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• 제1권
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• pp.20-25
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• 1962

쌀바구미가 현미의 함수량에 미치는 영향을 조사하여 다음과 같은 결과를 얻었다. A. R.H. $75\%\; 28^{\circ}C$에 있어서의 함수량의 증가 1) 100, 200, 500개체의 쌀바구미에 의하여 산란된 집단에 의하여 4주간에 사수량은 무곤충구에 비하여 $0.4\%,\;1\%,\;3.3%\$의 증가가 있었다. 2) 최대함수량은 500개체구에서 4주후에 $16.26\%$, 최소 100개체구에서 $14.86\%$였다. 3) 현미함수량의 증가는 현미내의 쌀바구미의 집단이 클수록 많다. B. $28^{\circ}C$에 있어서의 함수량의 층위적 변동 1) 무곤충구에 있어서는 함수량은 계속하여 감소하며 12주후에 있어서는 $10.66\%,\; 10.65\%,\; 12,21\%$가 되였다. 2) 실험구에 있어서는 상층을 제외하면 함수량은 12주후에는 최초의 함수량보다 증가하였으며 중층이 $15.64\%$, 하층이 $41.55\%$였다. 3) 대조구, 실험구 모두 상층에 갈수록 공중에의 수분탈취가 심하여 함수량은 하층보다 적었다. 4) 현미함수량의 증가는 곤충의 활동 급 미생물의 활동에 의한 것이라고 생각된다. 5) 쌀바구미의 집단은 어펄 특정한 층에 집합하는 일은 없으나 하층의 현미의 변질에 따라 상층으로 이동한다. 6) 현미내 온도는 대조구에 있어서는 환경온도와의 차가 적으며 낮은 것이 보통이나 실험구에 있어서는 높은 것이 보통이며 하층은 상층보다 높았다. 7) (6)에서와 갈은 온도의 차의 원인은 곤충의 호흡열 급 미생물의 분해열이 그 원인이라고 생각된다.

• Progress in Superconductivity
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• 제13권2호
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• pp.133-138
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• 2011

To reduce the processing cost of the single grain REBCO (RE: Rare-earth elements) bulk superconductors, a cost-effective process should be developed. One possible way of developing the cost-effective process is the use of low-cost precursor powders. In this study, the single grain YBCO superconductors were fabricated using a home made powder. $YBa_2Cu_3O_{7-y}$ (Y123) powders were synthesized at $850-900^{\circ}C$ in air by the powder calcination method with repeated crushing and heat treatment steps. The processing parameters for the fabrication of single grain Y123 bulk superconductors, $T_{max}$ (maximum temperature), $T_p$ (peritectic temperature) and a cooling rate through $T_p$ were optimized. To enhance the flux pinning capacity of the single grain Y123 samples, $Y_2BaCuO_5$ (Y211) particles were dispersed in the Y123 matrix by adding $Y_2O_3$ powder to the calcined Y123 powder. Applying the optimized processing condition, the single grain Y123 superconductors with $T_c=91\;K$ and $J_c=1.5{\times}10^4\;A/cm^2$ at 2 T were successfully fabricated using a home made powder. The levitation forces and trapped magnetic field at 77 K measured using a Nd-B-Fe permanent magnet of 5300 G were 47 N and 3000 G, respectively, which are comparable to those obtained for the samples fabricated using a commercial grade Y123 powders.

• 열처리공학회지
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• 제3권4호
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• pp.10-22
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• 1990

A study has been investigated on the effect of mechanical properties (tension strength, rotary bending fatigue strength, wear resistance, hardness) according to the carbide particle size variation by the treatment of 1) quenching tempering, and 2) quenching, subzero treatment and tempering. The material used in this investigation was a typical bearing steel, high C high Cr, AISI E 52100. The result obtained in this study were as follows : (1) Finer the carbide particle size increasing the hardness and retained austenite in same quenching condition. (2) Finer the carbide particle size reduced the tension and rotary bending fatigue which were resulted from austenite grain growth and carbide precipitation on grain boundry that induced by carbide refine heat treatment. (3) Finer the carbide particel size increasing the wear resistance which were resulted by uniform distribution of carbide and increased hardness induced by microstructural uniform hardenability of matrix. (4) When the carbide particles were refinded, subzero treatment is effective only wear resistance and hardness.