• 한국주조공학회지
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• 제10권1호
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• pp.31-42
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• 1990

The full mould casting process in one of the newly developed techniques which has many advantages. Unbonded sand mould has been prepared for the major mould and $CO^2$ gas mould has been used occasionally for comparison. Patterns were built up with expanded polystyrene and coated with three different materials. Silica, graphite and zircon were used for the coating layer. The effects on fluidity and temperature loss of molten metals were investigated. The molten metals were Al-5% Si alloy, Cu-30% Zn alloy and gray iron of approximately 4.0% of carbon equivalent. Experimental variables were runner section area, superheat, sprue height, coating materials, coating thickness and apparent density of EPS pattern. The effects of coating materials on fluidity and temperature loss of the molten metals during transient pouring are summarized as follows : As runner section area, superheat and sprue height increased, fluidity increased. Temperature loss decreased as runner section area and sprue height increased. However, reversed effects were observed in the case of superheat increment. The coating materials decreased the fluidity of each alloy in the order of silica, graphite and zircon. Zircon brought to the highest temperature loss among the coating materials used. The fluidity increased in the order gray iron, Cu-30% Zn and Al-5% Si alloy while temperature loss in the reverse order. Especially in case of reduced pressure process, the fluidity was increased apparently. Al-5% Si alloy showed the lowest temperature loss among the alloys. The increment of the apparent density of EPS pattern resulted in the fluidity decrease and temperature loss increase. The relation between fluidity and temperature loss of each alloy can be expressed by the following equation within the coating thickness limit of 0.5-1.5㎜. F^*={\frac{a}{T^*-b}}-c$ where, $F^*$ : fluidity in the Full mould, $T^*$ : temperature loss in the mould. a : parameter for full mould. b, c : constants.

• 대한기계학회논문집B
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• 제33권6호
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• pp.389-395
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• 2009

A specially designed flat plate was mounted vertically over the axial line in the wind tunnel of the Pusan National University. Strain balances were mounted in the trailing part of the plate to measure the skin friction drag over removable insertions of $0.55{\times}0.25m^2$ size. A set of the insertions was designed and manufactured: 3 mm thick polished metal surface and three compliant surfaces. The compliant surfaces were manufactured of a silicone rubber Silastic$^{(R)}$ S2 (Dow Corning company). To modify the viscoelastic properties of the rubber, its composition was varied: 90% rubber + 10% catalyst (standard), 92.5% + 7.5% (weak), 85% + 15% (strong). Modulus of elasticity and the loss factor were measured accurately for these materials in the frequency range from 40 Hz to 3 kHz. The aging of the materials (variation of their properties) for the period of one year was documented as well. Along with the drag measurement using the strain balance, velocity and pressure were measured for different coating. The strong compliant coating achieved 5% drag reduction within a velocity range $20{\sim}40$ m/s while standard and weak coatings increased drag reduction.

• 한국신뢰성학회지:신뢰성응용연구
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• 제17권1호
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• pp.78-82
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• 2017

Purpose: The purpose of this study is to evaluate failure characteristic and mechanism of four commercial water-repellent coatings for elevated temperature machinery applications. Method: Thermal degradation was performed for up to 64 thermal cycles. 1 cycle consists of 15 minute holding at 523K under 300rpm revolution and 15 minute-natural cooling. Contact angle was measured and microstructure of the coating layer was observed by using a scanning electron microscope. Results: Four kinds of commercial repellent coating showed hydrophobic or super-hydrophobic property implying that all coatings are suitable for room temperature application. Contact angle of three kinds of commercial coatings decreased rapidly after thermal exposure, while only one specimen having hydrophobic surface showed extremely slow degradation. Conclusion: Observed decrease in contact angle of the coatings were attributed to formation of macro-sized pores and disappearance of micro-protrusion during thermal exposure. Optimum water-repellent coating needs to be selected under the consideration of initial contact angle as sell as service temperature.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2014년도 제46회 동계 정기학술대회 초록집
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• pp.205.2-205.2
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• 2014

The effects of ion beam mixing of a SiC film coated on super alloys (hastelloy X substrates) were studied, aiming at developing highly sustainable materials at above $900^{\circ}C$ in decomposed sulfuric acid gas (SO2/SO3/H2O) channels of a process heat exchanger. The bonding between two dissimilar materials is often problematic, particularly in coating metals with a ceramics protective layer. A strong bonding between SiC and hastelloy X was achieved by mixing the atoms at the interface by an ion-beam: The film was not peeled-off at ${\geq}900^{\circ}C$, confirming excellent adhesion, although the thermal expansion coefficient of hastelloy X is about three times higher than that of SiC. Instead, the SiC film was cracked along the grain boundary of the substrate at above $700^{\circ}C$. At ${\geq}900^{\circ}C$, the film was crystallized forming islands on the substrate so that a considerable part of the substrate surface could be exposed to the corrosive environment. To cover the exposed areas and cracks multiple coating/IBM processes have been developed. An immersion corrosion test in 80% sulfuric acid at $300^{\circ}C$ for 100 h showed that the weight retain rate was gradually increased when increasing the processing time.

• The Journal of Advanced Prosthodontics
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• 제12권3호
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• pp.157-166
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• 2020

PURPOSE. The aim of this study was to evaluate the clinical performance and reliability of plasma sprayed nanostructured zirconia (NSZ) coating. MATERIALS AND METHODS. This study consisted of three areas of analysis: (1) Mechanical property: surface roughness of NSZ coating and bond strength between NSZ coating and titanium specimens were measured, and the microstructure of bonding interface was also observed by scanning election microscope (SEM). (2) Biocompatibility: hemolysis tests, cell proliferation tests, and rat subcutaneous implant test were conducted to evaluate the biocompatibility of NSZ coating. (3) Mechanical compatibility: fracture and artificial aging tests were performed to measure the mechanical compatibility of NSZ-coated titanium abutments. RESULTS. In the mechanical study, 400 ㎛ thick NSZ coatings had the highest bond strength (71.22 ± 1.02 MPa), and a compact transition layer could be observed. In addition, NSZ coating showed excellent biocompatibility in both hemolysis tests and cell proliferation tests. In subcutaneous implant test, NSZ-coated plates showed similar inflammation elimination and fibrous tissue formation processes with that of titanium specimens. Regarding fatigue tests, all NSZ-coated abutments survived in the five-year fatigue test and showed sufficient fracture strength (407.65-663.7 N) for incisor teeth. CONCLUSION. In this study, the plasmasprayed NSZ-coated titanium abutments presented sufficient fracture strength and biocompatibility, and it was demonstrated that plasma spray was a reliable method to prepare high-quality zirconia coating.

• Corrosion Science and Technology
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• 제6권6호
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• pp.286-290
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• 2007

Biocompatible Hydroxy apatite (HAp) coatings on metallic substrate by plasma spray techniques have been developed. Long-term credibility of plasma spray HAp coatings has been evaluated in physiological saline by electrochemical measurements. It was found that the corrosion resisitance of SUS316L based HAp/Ti conbined coatings was excellent even after more than 10 weeks long-term immersion. It was shown that postal heat treatment improved both the crystallinity and corrosion resistance of HAp. By lowering cooling rate during heat treatment process, less cracks produced in HAp coating layer, which lead to higher credibility of HAp during immersion in physiological saline. The ICP results showed that the dissolution level of substrate metallic ions was low and HAp coatings produced in this research can be acceptable as biocompatible materials. Also, the concentration of dissolved ions from HAp coatings with postal heat treatment was lower compared to those from samples without postal heat treatment. The adherence of HAp coatings with Ti substrate and other mechanical properties were also assessed by three-point bending test. The poor adhesion of HAp coating to titanium substrate can be improved by introducing a plasma spray titanium intermediate layer.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2005년도 추계학술대회 논문집 Vol.18
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• pp.260-261
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• 2005

The heterolayered thick/thin structure consisting of $Pb(Zr_{0.52}Ti_{0.48})O_3$ and $BaTiO_3(BT)$ were fabricated by a sol-gel process. PZT powders, prepared by the sol-gel method, were mixed with an organic vehicle and the PZT thick films were fabricated by the screen printing techniques on alumina substrate with Pt electrodes. The microstructural and dielectric characteristics of the stacked heterolayered PZT/BT/PZT films were investigated by varying the number of coating $BaTiO_3$ layers. The existence of a $BaTiO_3$ layer between the PZT thick films of the tri-layer $Pb(Zr_xTi_{1-x})O_3/BaTiO_3/Pb(Zr_xTi_{1-x})O_3$thick/thin/thick film can greatly improve the leakage current properties of the PZT thick films. The average thickness of a PZT(5248)/$BaTiO_3$ heterolayered thick/thin film was 25$\mu$m. The relative dielectric constant and dielectric loss of the PZT(5248)/$BaTiO_3$-3 heterolayered thin film coated three times were 1087 and 1.00% at 1[MHz].

• Journal of Welding and Joining
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• 제34권4호
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• pp.40-47
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• 2016

The Zn coating on automotive galvanized steel sheets can improve corrosion resistance. However, the boiling temperature of Zn is lower than the melting temperature of steel and it causes well-known spatter and porosity problem. One of most prominent solutions is a pretreatment of Zn coating by an additional welding arc prior to the main welding process. In this research, GTA and GMA are selected as heat sources for pretreatment and main welding processes, respectively. The authors suggested three possible mechanisms to reduce weld defects by the GTA pretreatment: (1) Formation of gap between the sheets; (2) Evaporation of Zn layer; (3) Oxidation of Zn layer. Among them, Zn Oxidation is the most important mechanism to reduce weld defects in the GTA-GMA hybrid process.

• 한국통신학회논문지
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• 제18권12호
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• pp.1935-1944
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• 1993

레이저 다이오드단면의 최적 무반사 코팅 조건을 활성층 두께의 함수로써 세가지 간단한 수치해석 방법을 사용하여 계산하였다. 세가지 간단한 수치해석 방법을 사용하여 얻은 결과가 서로 가른 것은 각 방법에서 사용한 레이저 다이오드내의 유효 굴절율이 다르기 때문이다. 또한 간단한 수치해석 방법의 정확성을 검토하기위하여 정확한 수치해석 결과와 그 결과들을 비교하였다. 레이저 다이오드의 유효 굴절율이 도과모드를 구성하는 각 편면파의 입사간도에 따라 변해 굴절율이 도파모드를 구성하는 각 평면파의 입사각도 따라 변화하도록 설정한 방법이 TE와 TM 모드에 대해서 또 활성층 굴절율과 클래딩층의 굴절율차가 작은 경우 클 경우 각각에 대하여 정확한 수치해석 결과와 잘 일치함을 알 수 있었다.

• 보존과학회지
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• 제26권2호
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• pp.149-156
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• 2010

금속 유물 코팅제로 사용되는 V-Flon은 함께 사용되는 용제인 YK-D80의 늦은 휘발성으로 작업에는 용이하나, 후처리로 유물을 접합하거나 복원처리 시, 코팅제가 완전 경화되지 않고 흘러나오는 문제점이 발생한다. 따라서 함침처리 후에 코팅제의 경화 속도를 가속시키기 위해 열풍 건조기에서 경화시키는 경우가 대부분이다. 이러한 V-Flon의 용제 휘발 속도의 문제점을 보완하고자 적용시키는 열풍 건조에 대한 문제점을 알아보고, 용제와 농도에 따른 변화 정도를 살펴보아 가장 효과적인 용제와 그 조성을 찾고자 하였다. 6 종류의 용제를 선정하였고 농도는 10%, 20%, 30%의 세 가지 농도로 함침 처리하여 시편을 제작하였다. 그리고 시편의 상태를 알아보기 위해서 금속 표면의 색상 및 광택 변화, 코팅막 두께 측정, 코팅 후의 부식 실험, 접촉각을 통한 내수성 측정을 실시하여 코팅제의 안정성을 평가하였다. 자연 건조와 열풍 건조의 비교 실험 결과, 열풍 건조는 외부의 강제 건조로 데이터 값이 불안정하여 균일하고 안정한 코팅막 형성에는 문제가 있음을 확인할 수 있었으며, 용제의 농도에 따른 실험 결과 V-Flon을 Xylene 용제를 이용하여 10% 용액으로 제조하여 사용할 경우, 얇은 코팅막에도 불구하고 높은 수분 차단성을 가지고 있었으며, 낮은 광택과 색변화를 나타내는 안정된 코팅막을 형성할 수 있었다.