• 전기화학회지
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• 제12권4호
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• pp.324-328
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• 2009

양극 (cathodes)과 음극 (anodes)이 서로 물리적으로 닿게되는 내부 단락 (internal short-circuit) 현상은 리튬이차전지 안전성 (safety) 이슈의 주요 원인으로 고려되고 있으며, 분리막 (separators)의 열 안정성 (thermal stability)에 의해 크게 영향을 받는 것으로 알려져 있다. 본 연구에서는 기존 폴리올레핀 (polyolefin) 계열 분리막에 비해 열 안정성이 현저히 개선된 세라믹 복합막 구조의 신규 분리막을 개발하여, 전지 내부 단락 발생을 억제하고자 하였다. 본 연구의 복합분리막은 알루미나 ($Al_2O_3$) 나노입자와 PVdF-HFP (polyvinylidene fluoride-hexafluoropropylene) 바인더로 구성된 세라믹 코팅층을, 폴리에틸렌 (polyethylene, PE) 분리막 양면에 도입시킴으로써 제조되었다. 세라믹 코팅층의 모폴로지는 코팅용액의 상전이 (phase inversion) 현상 제어를 통해 결정되었으며, 비용매 (물) 함량이 증가함에 따라 기공크기 및 기공구조가 보다 더 발달되었다. 이러한 세라믹 코팅층의 기공구조 변화는 복합분리막의 열 안정성 및 전기화학특성에 큰 영향을끼치는 것으로 관찰되었으며, 이를 상전이 현상 관점에서 체계적으로 해석하였다.

• 대한기계학회논문집A
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• 제38권12호
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• pp.1427-1430
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• 2014

열차폐 코팅은 고온 화염의 열이 블레이드의 모재에 직접 전달되는 것을 막는 역할을 하며, 세라믹 재질의 탑코팅층과 금속 모재간 결합력을 증가시켜주는 본드코팅층으로 이루어져있다. 이러한 열차폐 코팅 기술로 인하여 블레이드 표면의 온도가 화염온도에 비해 약 $100{\sim}170^{\circ}C$정도 낮아지게 된다. 이러한 열차폐 코팅은 금속모재와 코팅층의 열팽창 계수의 차이로 인해 내부 응력이 발생하게 되며, 블레이드의 형상 및 위치에 따라 발생하는 응력이 다르다. 따라서 본 논문에서는 열차폐코팅의 내구성 시험에 보편적으로 사용되는 코인형 시험편에 대하여 모재의 곡률에 따른 유한요소해석을 수행하고 열차폐 코팅에서 발생하는 내부 응력변화를 고찰하였다. 그 결과 탑코팅에 최저응력이 발생할 때의 곡률을 도출하였고 최저응력에서의 곡률과 차이가 커질수록 발생하는 응력이 커짐을 확인하였다.

• Korean Chemical Engineering Research
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• 제49권6호
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• pp.710-714
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• 2011

본 연구에서는 열 플라스마 용사 코팅 법을 사용하여 고체산화물 연료전지에서 사용되는 $La_{0.8}Ca_{0.2}CrO_{3}$(LCC), $La_{0.8}Sr_{0.2}CrO_{3}$(LSC), $La_{0.8}Ca_{0.2}CrO_{0.9}Co_{0.1}O_{3}$(LCCC) 세라믹 연결재를 코팅하여 코팅 층의 특성평가를 수행하였다. 열 플라즈마 코팅에 앞서 각 세라믹 연결재 입자의 특성평가를 위해 X선 회절, 미세 구조, 입자 측정 및 비표면적 분석을 수행하였다. 세라믹 연결재 입자의 특성평가 후, 열 플라스마 용사 코팅 법을 사용하여 연료극 지지체 위에 코팅하였으며, 코팅 층의 특성을 평가하기 위해 코팅 층의 표면, 파단면 분석, 가스 누출 속도 및 전기 전도도 측정을 수행하였다. 이러한 특성 평가 결과를 바탕으로 열 플라스마 용사 코팅 법을 통해 코팅된 LCCC 코팅 층이 고체산화물 연료전지의 세라믹 연결재로서 적합함을 확인하였다.

• 한국수소및신에너지학회논문집
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• 제21권3호
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• pp.201-206
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• 2010

In present work, $La_{0.8}Ca_{0.2}CrO_3$ (LCC) ceramic interconnect layer for SOFC was prepared by using thermal plasma spray coating process. The LCC powders were synthesized by Pechini method and calcined at the temperature of $1000^{\circ}C$. The prepared LCC powder was characterized by x-ray diffraction (XRD), scanning electron microscopy (SEM), particle counter, BET analysis, respectively. In addition, basic and essential properties of LCC layer coated by thermal plasma spray coating process such as the morphology of surface and cross section for coated layer, gas leak rate, and electrical conductivity were analyzed and discussed. Based on these experimental results, it can be concluded that the LCC layer coated by thermal plasma spray coating process can be suitable as a ceramic interconnect of SOFC operated at $800^{\circ}C$.

• 한국재료학회지
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• 제19권12호
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• pp.649-656
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• 2009

Inorganic oxide colloids dispersed in alcohol were applied to a stainless steel substrate to produce oxide coatings for the purpose of minimizing emissive thermal transfer. The microstructure, roughness, infrared emissive energy, and surface heat loss of the coated substrate were observed with a variation of the nano oxide sol and coating method. It was found that the indium tin oxide, antimony tin oxide, magnesium oxide, silica, titania sol coatings may reduce surface heat loss of the stainless steel at 300${\circ}C$. It was possible to suppress thermal oxidation of the substrate with the oxide sol coatings during an accelerated thermal durability test at 600${\circ}C$. The silica sol coating was most effective to suppress thermal oxidation at 600${\circ}C$, so that it is useful to prevent the increase of radiative surface heat loss as a heating element. Therefore, the inorganic oxide sol coatings may be applied to improve energy efficiency of the substrate as the heating element.

• Tribology and Lubricants
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• 제30권2호
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• pp.108-115
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• 2014

The friction behaviors of bulk amorphous thermal spray coating (BAC) and second phase-reinforced composite coatings using a high velocity oxy-fuel spraying process were investigated using a ball-on-disk test rig that slides against a ceramic ball in an atmospheric environment. The surface temperatures were measured using an infrared thermometer installed 50 mm from the contact surface. The crystallinities of the coating layers were determined using X-ray diffraction. The morphologies of the coating layers and worn surfaces were observed using a scanning electron microscope and energy-dispersive spectroscopy. The results show that the friction behavior of the monolithic amorphous coating was sensitive to the testing conditions. Under lower than normal loads, a low and stable friction coefficient of about 0.1 was observed, whereas under a higher relative load, a high and unstable friction coefficient of greater than 0.3 was obtained with an instant temperature increase. For the composite coatings, a sudden increase in friction coefficient did not occur, i.e., the transition region did not exist and during the friction test, a gradual increase occurred only after a significant delay. The BAC morphology observations indicate that viscous plastic flow was generated with low loads, but severe surface damage (i.e., tearing) occurred at high loads. For composite coatings, a relatively smooth surface was observed on the worn surface for all applied loads.

• Structural Engineering and Mechanics
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• 제83권4호
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• pp.551-561
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• 2022

In this paper, the effect of fire conditions according to ISO 834 standard on the behavior of carbon fibre-reinforced plastic (CFRP) reinforced steel beams coated with gypsum-based mortar has been investigated numerically. To study the efficiency of these beams, 3D coupled temperature-displacement finite element analyzes have been conducted. Mechanical and thermal characteristics of three different parts of composite beams, i.e., steel, CFRP plate, and fireproof coating, were considered as a function of temperature. The interaction between steel and CFRP plate has been simulated employing the adhesion model. The effect of temperature, CFRP plate reinforcement, and the fireproof coating thickness on the deformation of the beams have been analyzed. The results showed that within the first 120 min of fire exposure, increasing the thickness of the fireproof coating from 1 mm to 10 mm reduced the maximum temperature of the outer surface of the steel beam from 380℃ to 270℃. This increase in the thickness of the fireproof layer decreased the rate of growth in the temperature of the steel beam by approximately 30%. Besides excellent thermal resistance and gypsum-based mortar, the studied fireproof coating method could provide better fire resistance for steel structures and thus can be applied to building materials.

• 한국분말재료학회지
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• 제24권2호
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• pp.102-107
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• 2017

Porous polytetrafluoroethylene (PTFE) thin films are fabricated by spin-coating using a dispersion solution containing PTFE powders, and their crystalline properties are investigated after thermal annealing at various temperatures ranging from 300 to $500^{\circ}C$. Before thermal annealing, the film is densely packed and consists of many granular particles 200-300 nm in diameter. However, after thermal annealing, the film contains many voids and fibrous grains on the surface. In addition, the film thickness decreases after thermal annealing owing to evaporation of the surfactant, binder, and solvent composing the PTFE dispersion solution. The film thickness is systematically controlled from 2 to $6.5{\mu}m$ by decreasing the spin speed from 1,500 to 500 rpm. A triboelectric nanogenerator is fabricated by spin-coating PTFE thin films onto polished Cu foils, where they act as an active layer to convert mechanical energy to electrical energy. A triboelectric nanogenerator consisting of a PTFE layer and Al metal foil pair shows typical output characteristics, exhibiting positive and negative peaks during applied strain and relief cycles due to charging and discharging of electrical charge carriers. Further, the voltage and current outputs increase with increasing strain cycle owing to accumulation of electrical charge carriers during charge-discharge.

• 대한금속재료학회지
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• 제50권7호
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• pp.539-544
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• 2012

Thermal shock behavior of TiN-coated SUS 304 substrate was investigated using a laser ablation method. By short surface ablation with a pulse Nd-YAG laser, considerable surface crack and spalling were observed, whereas there were few oxidation phenomena, such as grain growth of TiN crystallites, nucleation and growth of $TiO_2$ crystallites, which were observed from the coatings quenched from $700^{\circ}C$ in a chamber. The oxygen concentration of the ablated coating surface with the pulse laser also had a lower value than that of the quenched coating surface by Auger electron spectroscopy and electron probe micro analysis. These results were attributed to the fact that the properties of the pulse laser method have a very short heating time and so the diffusion time for oxidation was insufficient. Consequently, it was verified that the laser thermal shock test provides a way to evaluate the influence of the thermal shock load reduced oxidation effect.

• 한국표면공학회지
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• 제51권5호
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• pp.297-302
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• 2018

The important drawback of hardware fasteners consisted of 304 stainless steel (STS) is a frequent galling caused by a combination of friction and adhesion between the sliding surface. To improve the anti-galling effect, Sn-Al coatings by a thermal diffusion have been developed. The thermal diffusion by pack cementation with an $AlCl_3$ activator at $250^{\circ}C$ for 1 hour produced an Sn-Al alloy coating layer with an average thickness of $9.9{\pm}0.5{\mu}m$ on the surface of 304 STS fasteners. Compared with the galling frequency of the 304 STS fasteners, Sn-Al coatings on the surface of 304 STS fasteners demonstrated about 2.8-time reduction of the galling frequency.