• 한국자동차공학회논문집
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• 제22권5호
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• pp.20-28
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• 2014

The high velocity oxygen fuel spraying (HVOF) is a kind of surface modification process technology to form the sprayed coating layer after spraying the powder to molten or semi-molten state by the ultra-high speed at the high-temperature heat source and conflicting with a substrate. It is desirable to melt completely the thermal spray powder in order to produce the coating layer with an optimal adhesion, however, because a semi-molten powder in a spray process has the low efficiency and become a factor that degrades the mechanical property by the inducement of pore-forming within the coating layer. To improve the wear resistance, corrosion resistance and heat resistance, in this study, the plungers of high-speed and ultra-high pressure reciprocating hydraulic pumps for oil and water used in ironwork are produced with $420J_2$ and the coating layers of plungers are formed by the powders of WC-Co-Cr and WC-Cr-Ni including the high hardness WC. The surface of these plungers is modified by the super-mirror face grinding machine using variable air pressure developed in this laboratory, and then the characteristics of cross-sectional microstructure, and surface roughness and hardness values between no operation and 100 days-operation are examined and made a comparison. The fine tops and bottoms on surface roughness curve of oil-hydraulic pump plunger sprayed by WC-Cr-Ni are molded more and higher than those of water-hydraulic pump sprayed by WC-Co-Cr because the plunger diameter of oil-hydraulic pump is 0.4 times smaller than that of water-hydraulic pump and the pressure of oil-hydraulic pump exerted on the plunger is operated with the 70 bars higher than that of water-hydraulic pump. As a result, it is found that the values of centerline average surface roughness and maximum height for oil-hydraulic pump plunger are bigger than those of water-hydraulic pump plunger.

• 한국재료학회지
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• 제4권6호
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• pp.687-694
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• 1994

선택적 LPE방법을 이용하여 (111)B GaAs 기판 상에 InP연속 박막을 성장하고 그 특성을 평가하였다. 적정 LPE성장조건으로 성장온도 $660^{\circ}C$, 과냉도 $5^{\circ}C$, 냉각속도 $0.4^{\circ}C$/min였으며, 연구된 온도 범위에서 성장온도가 증가할수록 표면형상이 개선되었고 ELO의 넓이가 증가하였다. Seed방향이 <112>방향에서 110-160$\mu \textrm{m}$ 정도의 최대 ELO 넓이가 얻어졌으며 60-80$\mu \textrm{m}$정도의 마스크 간격에서 연속박막을 용이하게 성장할 수 있었다. LPE 성장초기에 기판 용해 현상이 발생하였으며 이에 따라 성장박막의 조성이 대략 $In_{0.85}Ga_{0.15}$As$_{0.01}P{0.99}$으로 변화하고 InP/GaAs계면 및 박막 표면형상이 거칠어졌으나 기판의 성장 부위가 제한됨에 따라 통상적인 LPE박막에 비교하여 매우 개선된 표면형상을 얻을 수 있었다. 두개의 성장융액을 이용하여 1차 박막성장 후 다시 InP 박막을 성장하는 2단성장 방법을 사용하여 순수한 InP/GaAs박막을 성장할 수 있었으며 단면 TEM분석 결과 SLPE성장박막으로 전파하는 활주전위는 산화막 마스크에 의해 효과적으로 차단됨을 알 수 있었다.

• 한국자동차공학회논문집
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• 제24권3호
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• pp.285-293
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• 2016

The high velocity oxygen fuel(HVOF) thermal spray is a kind of surface modification techniques to produce the sprayed coating layer. This process is to form the coating layer after spraying the powder to molten or semi-molten state by the ultra-high speed at the high-temperature heat source and conflicting with a substrate. The efficiency of thermal spraying is dropped, however, because the semi-molten powder in a spray process become a factor that degrades the mechanical property by the formed pore within the coating layer. Therefore, it is necessary to melt completely the thermal spray powder in order to produce the coating layer with an optimal adhesive force. In this study, to improve the wear resistance, corrosion resistance and heat resistance, the plungers of high-speed and ultra-high pressure reciprocating hydraulic pumps used in ironworks are manufactured with STS $420J_2$ and are coated by the powders of WC-Co-Cr and WC-Cr-Ni including the WC of high hardness using a HVOF thermal sprayer developed in this laboratory. These are called by the surface-modified plungers. The surface roughness, hardness, and surface and cross-sectional microstructure of these two surface-modified and conventional ceramic plungers are measured and compared before operation with after operation for 100 days. It is found that the values of centerline average surface roughness and maximum height for conventional ceramic plunger are 9.5 to 10.8 and 5.2 to 5.7 times higher than those of surface-modified ones coated by WC-Co-Cr and WC-Cr-Ni because the fine tops and bottoms on surface roughness curve of conventional ceramic plunger are approximately 100 times higher than those of surface-modified ones. In addition, the pores and scratches in the surface microstructure are considerably formed in the order of conventional ceramic, WC-Cr-Ni and WC-Co-Cr surface-modified plungers. The greater the WC content of high hardness powder is less the change in the plunger surface.

• 공업화학
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• 제16권1호
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• pp.52-60
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• 2005

본 연구에서는 용융법에 의한 저밀도폴리에틸렌 나노복합재료를 제조하였으며, 구조변화, organo-clay의 분산정도, 열적 특성 및 난연 특성을 조사하였다. LDPE/PE-g-MA/organo-clay의 조성비가 90/10/1~10 (w/w/w)일 때, XRD 분석 결과 clay 층간간격이 증가함을 알 수 있었으며, TEM을 이용하여 organo-clay의 분산을 관찰하였는데, 대체적으로 organo-clay가 일정한 방향성을 가지며 잘 분산되어 있음을, 즉 삽입형(intercalation) 나노복합체가 형성되었음을 확인할 수 있었다. 또한 LDPE 나노복합재료의 분해온도가 순수한 LDPE에 비해 약 $80^{\circ}C$ 정도 상승함으로써 열적특성이 현저히 증가함을 알 수 있었고, organo-clay 5.0 wt% 범위 내에서 organo-clay의 함량이 증가함에 따라 LOI가 증가함을, 그 이상에서는 더 이상의 LOI 증가를 보이지 않음을 알 수 있었다.

• 한국산학기술학회논문지
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• 제15권6호
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• pp.4039-4045
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• 2014

전자선 조사 폴리프로필렌과 블랜드의 결정화 거동은 고분자 가공시 중요한 변수중 하나이다. 저밀도폴리에틸렌(linear low density polyethylene, LDPE) 함량에 따라 폴리프로필렌(polypropylene, PP)/LDPE 블렌드를 이축압출기를 이용하여 제조하였다. 조사에 의한 가교반응을 용이하게 하기위해 가교조제로 trimethylolpropane-trimetacrylate (TMPTMA)를 PP/LDPE 블렌드 제조시 첨가하였다. PP/LDPE 블랜드의 조사가교 효율에 대한 LDPE 함량의 영향을 평가하였다. 조사시료의 비등온 결정화과정과 결정구조를 DSC, X-선회절분석(X-ray diffraction, XRD), 그리고 편광현미경(polarized optical microscope, POM)을 이용하여 분석하였다. 조사 후 시료의 용융온도가 감소하는 것은 조사에 의한 PP 사슬의 절단에 의한 것으로 판단된다. Ozawa 지수, n이 4일 때 구형, 3일 때 디스크형, 2일 때 로드형의 결정구조를 나타낸다. Ozawa 분석 결과, 순수 PP의 n 값은 3.8, 30 wt%의 LDPE를 포함하는 시료의 n은 2.3을 나타내었다. LDPE 첨가와 조사에 의해 PP의 결정구조가 구형에서 disk나 rod형으로 변화하는 것을 Ozawa 분석과 POM을 통해 확인하였다. XRD 스펙트럼의 $16.1^{\circ}$에서 나타나는 ${\beta}$ 형 결정구조가 조사 후 시편에서 사라지는데, 이는 가교결합에 의한 것으로 해석할 수 있다.

• 한국안광학회지
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• 제20권1호
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• pp.1-7
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• 2015

목적: 본 연구에서는 안경테 가공공정별 셀룰로오스 아세테이트(CA) 판재의 물성을 분석 함으로써 최종 완제품의 물성 최적화를 위해 가공조건과 CA판재 물성과의 상관관계를 조사하는 것을 연구목적으로 한다. 방법: 안경테 가공공정별 CA 판재의 물성 변화를 확인하기 위해, 벤딩 공정, 바렐 공정 및 초음파 세척공정과 동일한 조건에서 제조된 판재의 물성이 평가되었다. 일련의 공정을 통해 제조된 판재의 물성은 광택도, 기계적 물성, 및 열적 특성을 통해 비교 분석되었다. 결과: 바렐 공정을 거친 CA 판재의 경우, 경도 및 기계적 물성이 증가함을 확인하였으며, 반면, 굽힘 강도 및 충격강도의 감소를 보였다. 이는 공정을 거치면서 CA 판재가 brittle한 특성을 보임을 의미한다. 또한 열분석 결과, 가소제 분해 온도 영역에서, 약 3% 내외의 가소제 감량을 확인하였다. 결론: 안경테 가공공정 중 바렐 공정이 CA 판재 물성에 급격한 영향을 미침을 확인하였고, 이는 가소제 총량의 감량에 기인한 현상으로 판단된다.

• 한국광학회지
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• 제15권4호
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• pp.361-368
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• 2004

콤팩트디스크(CD-R; Compact DiskRecordable)를 성분별로 분리하여 제작하고, 다층 박막 구조를 만들어서 레이저빔의 에너지를 변화시켜 가면서 조사하여 각 성분 층에서의 최적 미소 점 마킹 조건과 홈 형성 과정에 관하여 연구하였다. 본 연구는 Q-스위치 Nd:YAG 레이저를 이용하여 준비된 각 시료의 표면에 27∼373 mJ 빔을 80 $\mu\textrm{m}$의 점적 크기로 조사하여 샘플에 형성된 흠 형태를 광학현미경(OM; Optical Microscope)과 광 결맞음 단층촬영기(OCT; Optical Coherence Tomography)로 비교-관찰하여 미소 점 마킹의 형성 과정을 분석하였다. 다층 박막에서 용융된 기판 층은 짧은 시간동안 충분한 열 흐름이 발생하여 증배의 형성을 야기하며, 반사 층과 염료 층 사이에 흡수된 에너지는 염료를 용융시키고 체적을 증가시켰으며, 증배가 식으면서 표면장력의 영향 및 레이저빔에 의한 순간적인 시편의 온도상승으로 기화와 반동압력에 의한 질량흐름 때문에 두 층의 경계면에서 홈과 외륜의 발생을 설명할 수 있었다. 따라서 다층 박막에서의 미소 점 마킹의 형성 과정은 표면장력, 용융 점성력, 층 두께, 다층 박막 성분 물질의 물리화학적ㆍ광학적 성질과 관계가 있음을 알 수 있었다.

• 한국재료학회지
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• 제23권6호
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• pp.309-315
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• 2013

$GdBa_2Cu_3O_{7-y}$(Gd123) powders were synthesized by the solid-state reaction method using $Gd_2O_3$ (99.9% purity), $BaCO_3$ (99.75%) and CuO (99.9%) powders. The synthesized Gd123 powder and the Gd123 powder with $Gd_2O_3$ addition ($Gd_{1.5}Ba_2Cu_3O_{7-y}$(Gd1.5)) were used as raw powders for the fabrication of Gd123 bulk superconductors. The Gd123 and Gd1.5 bulk superconductors were fabricated by sintering or a top-seeded melt growth (TSMG) process. The superconducting transition temperature ($T_{c,onset}$) of the sintered Gd123 was 93 K and the transition width was as large as 20 K. The $T_{c,onset}$ of the TSMG processed Gd123 was 82 K and the transition width was also as large as 12 K. The critical current density ($J_c$) at 77 K and 0 T of the sintered Gd123 and TSMG processed Gd123 were as low as a few hundreds A/$cm^2$. The addition of 0.25 mole $Gd_2O_3$ and 1 wt.% $CeO_2$ to Gd123 enhanced the $T_c$, $J_c$ and magnetic flux density (H) of the TSMG processed Gd123 sample owing to the formation of the superconducting phase with high flux pinning capability. The $T_c$ of the TSMG processed Gd1.5 was 92 K and the transition width was 1 K. The $J_cs$ at 77 K (0 T and 2 T) were $3.2{\times}10^4\;A/cm^2$ and $2.5{\times}10^4\;A/cm^2$, respectively. The H at 77 K of the TSMG-processed Gd1.5 was 1.96 kG, which is 54% of the applied magnetic field (3.45 kG).

• 원예과학기술지
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• 제34권6호
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• pp.912-923
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• 2016

Watermelon production is often limited by powdery mildew in areas with a large daily temperature range. Development of resistant watermelon cultivars can protect against powdery mildew; however, little is known about the characteristics of its causal agents. Here, we identified the genus and race of a causal pathogen of powdery mildew in Ansung province of South Korea, and developed molecular markers for the generation of resistant watermelon cultivars. The causal pathogen was determined to be Podosphaera xanthii based on multiple sequence alignments of internal transcribed spacers (ITS) of rDNA. The physiological race was identified as 1W, and the Ansung isolate was named P. xanthii 1W-AN. Following inoculation with the identified P. xanthii 1W-AN, we found inheritance of the resistant gene fitting a single dominant Mendelian model in a segregated population ('SBA' ${\times}$ PI 254744). To develop molecular markers linked to fungus-resistant loci, random amplified polymorphic DNA (RAPD) was accomplished between DNA pooled from eight near-isogenic lines (NILs; $BC_4F_6$), originated from PI 254744 and susceptible 'SBB' watermelon. After sequencing bands from RAPD were identified in all eight NILs and PI254744, 42 sequence-characterized amplifiedregion (SCAR) markers were developed. Overall, 107 $F_2$ plants derived from $BC_4F_6$ NIL-1 ${\times}$ 'SBB' were tested, and one SCAR marker was selected. Sequence comparison between the SCAR marker and the reference watermelon genome identified three Nco I restriction enzyme sites harboring a single nucleotide polymorphism, and codominant cleavage-amplified polymorphic site markers were subsequently developed. A CAPS marker was converted to a high-resolution melt (HRM) marker, which can discriminate C/T SNP (254PMR-HRM3). The 254PMR-HRM3 marker was evaluated in 138 $F_{2:3}$ plants of a segregating population ('SBA' ${\times}$ PI254744) and was presumed to be 4.3 cM from the resistance locus. These results could ensure P. xanthii 1W-AN resistance in watermelon germplasm and aid watermelon cultivar development in marker-assist breeding programs.

• 한국재료학회지
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• 제18권6호
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• pp.339-346
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• 2008

Single-crystal $ZnIn_2S_4$ layers were grown on a thoroughly etched semi-insulating GaAs (100) substrate at $450^{\circ}C$ with a hot wall epitaxy (HWE) system by evaporating a $ZnIn_2S_4$ source at $610^{\circ}C$. The crystalline structures of the single-crystal thin films were investigated via the photoluminescence (PL) and Double-crystal X-ray rocking curve (DCRC). The temperature dependence of the energy band gap of the $ZnIn_2S_4$ obtained from the absorption spectra was well described by Varshni's relationship, $E_g(T)=2.9514\;eV-(7.24{\times}10^{-4}\;eV/K)T2/(T＋489K)$. After the as-grown $ZnIn_2S_4$ single-crystal thin films was annealed in Zn-, S-, and In-atmospheres, the origin-of-point defects of the $ZnIn_2S_4$ single-crystal thin films were investigated via the photoluminescence (PL) at 10 K. The native defects of $V_{Zn}$, $V_S$, $Zn_{int}$, and $S_{int}$ obtained from the PL measurements were classified as donor or acceptor types. Additionally, it was concluded that a heat treatment in an S-atmosphere converted $ZnIn_2S_4$ single crystal thin films into optical p-type films. Moreover, it was confirmed that In in $ZnIn_2S_4$/GaAs did not form a native defects, as In in $ZnIn_2S_4$ single-crystal thin films existed in the form of stable bonds.