• Composites Research
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• 제33권3호
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• pp.101-107
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• 2020

본 논문에서는 탄화규소로 코팅된 탄소-탄소복합재료의 단열 특성을 고찰하였다. 탄소-탄소 복합재료 상에 탄화규소를 화학증착법(CVD)법으로 코팅하였다. 먼저 탄화규소로 코팅한 복합재와 코팅되지 않은 복합재에 대해, 공기 중에서 1350℃의 온도를 급작스럽게 부가하였을 때의 단열특성을 서로 비교하는 연구를 수행하였다. 또한 본 연구에서는 최대 1700℃ 및 2000℃의 온도에 복합재의 표면을 노출시키는 고온 버너실험을 수행하였다. 버너실험 전, 후의 무게를 측정하여 무게변화를 고찰하였다. 고온 버너실험 후 탄소-탄소 복합재 및 탄화규소로 코팅된 복합재의 손상여부를 비교, 고찰하였다. 그 결과 2000℃의 온도에 노출 시 탄화규소 코팅재에서 박리, 균열, 공동 등의 결함손상들이 발견되었으나, 고온으로부터 탄소-탄소 복합재를 보호하는데 효과적이었다.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2009년도 제7회 압연 심포지엄
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• pp.65-71
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• 2009

The process of cold rolling is becoming more severe with the increase in the production of high tensile steel strip as a result of increased demand. Consequently, there is a need to develop work roll materials with better resistance to wear and roll failure. DOOSAN has developed an improved in-house 5%Cr alloy, New HSR1, with properties superior to the existing in- house 5%Cr alloy, Old HSR1. Test alloys were designed with controlled amounts of Si and Mn based on Old HSR1 and an optimum alloy was chosen based on thermal shock tests. A prototype work roll was manufactured with New HSR1, and properties of test specimens were evaluated. The results indicated that New HSR1 has better properties than Old HSR1. After application of New HSR1 work rolls, productivity increased due to advanced resistance to wear and roll failure.

• 한국레이저가공학회지
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• 제12권3호
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• pp.18-22
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• 2009

Experimental results for the laser shock peening of stainless steels, duplex stainless steel and STS304, for the enhancement of surface hardness are reported. A high power Nd:YAG laser (532 nm, 2nd harmonics) was used to irradiate the workpiece in water at the irradiances of 5, 10, $15\;GW/cm^2$. The surface of a workpiece was covered with Fe or Al foil for protection of the original surface and reduction of laser reflection. The laser pulse densities were varied from $25\;pulse/mm^2$ to $75\;pulse/mm^2$. In the case of the STS304, the surface hardness increased with increasing pulse density and the maximum increase of about 29% was achieved using Fe foil at $10\;GW/cm^2$ and $75\;pulse/mm^2$ conditions. The maximum increase in surface hardness of duplex stainless steel was about 8% at $10\;GW/cm^2$ and $75\;pulse/mm^2$ with also Fe foil. In the case of the Al foil, less increase of surface hardness was obtained, possibly due to the thermal expansion effect.

• 한국항해항만학회:학술대회논문집
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• 한국항해항만학회 2000년도 추계학술대회논문집
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• pp.116-119
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• 2000

The advantage of plasma-sprayed coating is their good resistance against thermal shock due to the porous state of the coated layer with a consequently low Youngs modulus. However, the existence of many pores with a bimodal distribution and a laminar structure in the coating reduces coating strength and oxidation protection of the base metals. In order to counteract these problems, there have been many efforts to obtain dense coatings by spraying under low pressure or vacuum and by controlling particle size and morphology of the spraying materials. The aim of the present study is to survey the effects of the HIP treatment between 1100 and 130$0^{\circ}C$ on plasma-sprayed oxide coating of A1$_2$O$_3$, A1$_2$O$_3$-SiO$_2$on the metal substrate (type C18N10T stainless steel). These effects were characterized by phase identification, Vickers hardness measurement, and tensile test before and after HIPing. These results show that high-pressure treatment has an advantage for improving adhesive strength and Vickers hardness of plasma-sprayed coatings.

• Journal of Microbiology and Biotechnology
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• 제20권7호
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• pp.1156-1162
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• 2010

During ethanol fermentation, bacterial strains may encounter various stresses, such as ethanol and acid shock, which adversely affect cell viability and the production of ethanol. Therefore, ethanologenic strains that tolerate abiotic stresses are highly desirable. Bacteria of the genus Deinococcus are extremely resistant to ionizing radiation, ultraviolet light, and desiccation, and therefore constitute an important pool of extreme resistance genes. The irrE gene encodes a general switch responsible for the extreme radioresistance of D. radiodurans. Here, we present evidence that IrrE, acting as a global regulator, confers high stress tolerance to a Zymomonas mobilis strain. Expression of the gene protected Z. mobilis cells against ethanol, acid, osmotic, and thermal shocks. It also markedly improved cell viability, the expression levels and enzyme activities of pyruvate decarboxylase and alcohol dehydrogenase, and the production of ethanol under both ethanol and acid stresses. These data suggest that irrE is a potentially promising gene for improving the abiotic stress tolerance of ethanologenic bacterial strains.

• 한국재료학회지
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• 제12권2호
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• pp.129-134
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• 2002

The optimum condition for fabricating cordierite disc type filter element was deduced. Cordierite monolith was used as starting material for filter element because it has many advantages such as high thermal shock resistance and good catalytic activity compared with $TiO_2$and SiC. The contents of organic additives and foaming agent were optimized to control the porosity and mechanical strength of cordierite filter. Among the required properties to be adopted as filter elements, the pressure drop and NOx removal efficiency were investigated depending on processing variables. It was found that pressure drop depends on particle size distribution of cordierite monolith and organic additives added as forming agent. The pressure drop at 5cm/sec of face velocity was in the range of 15~655mm$H_2O$ at room temperature. The NOx removal efficiency of catalytic filter with $V_2O_5$ as catalyst was over 85% at $450^{\circ}C$.

• 한국세라믹학회지
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• 제27권3호
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• pp.329-336
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• 1990

In this investigation, bar-shaped specimens which consisted of three layers are prepared to study the effects of residual compressive stress on the mechanical properties in ZTA. The outer layers contained Al2O3 and unstabilized ZrO2 and the central layer contained Al2O3 and stabilized ZrO2(with 5.10wt% Y2O3). When cooled from the sintering temperature, some of zirconia in the outer layers transformed to the monoclinic form while zirconia in the central layer was retained in the tetragonal form. The transformation which induces to dilatational expansion led to the estabilishmenet of compressive stress in the outer layers and balances tensile stress in the central layer. Decrease of outer layer thickness(for a fixed total thickness)increases residual compressive stress. Because of residual compressive stress in the outer layers, the fracture toughness of outer layers of 3-layers composite is 10.21 Mpam1/2, which is increased to 25% above in comparison with 1-layer specimens in ZTA. Also, the 3-layers composite is believed to exhibite greater fracture resistance in contact damage environment from thermal shock test.

• 한국세라믹학회지
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• 제25권2호
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• pp.131-135
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• 1988

The microstructural changes in partially stabilized MgO-ZrO2 alloys during heat treatment and mechanical properties of ZrO2(Y2O3)/Al2O3 systems have been studied. 9mol% MgO-ZrO2 powders were sintered at 1800$^{\circ}C$ for 4 hours and these specimens were aged at 1420$^{\circ}C$ and 1100$^{\circ}C$ secondly. These specimens have high thermal shock resistance and high toughness. The bend strength of Y-PSZ/Al2O3 composites conventially sintered were increased by HIP from 650MPa to 980MPa.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2000년도 추계학술대회 논문집
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• pp.116-119
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• 2000

The advantage of plasma-sprayed coating is their good resistance against thermal shock due to the porous state of the coated layer with a consequently low Youngs modules. However, the existence of many pores with a bimodal distribution and a laminar structure in the coating reduces coating strength and oxidation protection of the base metals. In order to counteract these problems, there have been many efforts to obtain dense coatings by spraying under low pressure or vacuum and by controlling particle size and morphology of the spraying materials. The aim of the present study is to survey the effects of the HIP treatment between 1100 and 130$0^{\circ}C$ on plasma-sprayed oxide coating of A1$_2$O$_3$, A1$_2$O$_3$-SiO$_2$ on the metal substrate (type C18N10T stainless steel). These effects were characterized by phase identification, Vickers hardness measurement, and tensile test before and after HIPing, These results show that high-pressure treatment has an advantage for improving adhesive strength and Vickers hardness of plasma- sprayed coatings.

• 한국재료학회지
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• 제24권5호
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• pp.249-254
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• 2014

Due to their unique properties, tungsten borides are good candidates for the industrial applications where certain features such as high hardness, chemical inertness, resistance to high temperatures, thermal shock and corrosion. In this study, conditions were investigated for producing tungsten boride powder from tungsten oxide($WO_3$) by self-propagating high-temperature synthesis (SHS) followed by HCl leaching techniques. In the first stage of the study, the exothermicity of the $WO_3$-Mg reaction was investigated by computer simulation. Based on the simulation experimental study was conducted and the SHS products consisting of borides and other compounds were obtained starting with different initial molar ratios of $WO_3$, Mg and $B_2O_3$. It was found that $WO_3$, Mg and $B_2O_3$ reaction system produced high combustion temperature and radical reaction so that diffusion between W and B was not properly occurred. Addition of NaCl and replacement of $B_2O_3$ with B successfully solved the diffusion problem. From the optimum condition tungsten boride($W_2B$ and WB) powders which has 0.1~0.9 um particle size were synthesized.