• Applied Chemistry for Engineering
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• v.18 no.5
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• pp.495-500
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• 2007

The inside wall of a coal gasifier is lined with refractory, and the corrosion of the refractory is an important factor affecting the refractory lifetime and the replacement period. This paper examines the changes in microstructure of a chromia refractory due to chemical reactions with slag having varying amounts of $Fe_2O_3$. Slag samples were prepared by adding $Fe_2O_3$ to KIDECO slag, and static corrosion experiments were carried out at $1550^{\circ}C$. The layer of $(Fe,Cr)_3O_4$ formation and the depth of Fe depletion in the infiltrating slag were determined. In addition, FactSage equilibrium calculations were carried out in order to determine the conditions of formation, and to compare with the experimental observations. In the sample exposed to KIDECO slag, which has about 10 wt% $Fe_2O_3$, the formation of $(Fe,Cr)_3O_4$ was not observed. As the $Fe_2O_3$ concentration in slag increased, $(Fe,Cr)_3O_4$ formation and Fe depletion depth increased. Increasing $Fe_2O_3$ concentration also made the slag/refractory interface indistinguishable. Equilibrium calculations predicted that higher $Fe_2O_3$ concentrations favor chromite formation at gasification temperatures. The chromite formation was most favorable when the amount of $Cr_2O_3$ was limited, as in the case of dissolved $Cr_2O_3$ in slag. When the concentration of $Fe_2O_3$ in slag was less than 20%, the formation of chromite was least favorable in the system with equal amounts of slag and refractory.

• Journal of the Korean Society for Heat Treatment
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• v.18 no.6
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• pp.383-393
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• 2005

본 고에서는 사출금형소재로 널리 사용되는 프리하든 강의 수명을 극대화 시킬 수 있는 열 표면처리 기술에 대해 소개하였다. 이러한 열 표면처리 기술 및 기술 적용시 고려해야할 점을 다시 정리해 보면, 제조하는 대상물을 고려한 최적 금형 재료의 선택 (표 1~3) 선택된 금형의 물성을 최적으로 구현할 수 있는 열처리 선택 (표 4) 금형의 사용 환경을 고려한 최적 열 표면처리 선택 (표 5) 질화 열처리에 의한 수명 향상 피로 수명이 중요한 경우 : 질화층 $100{\mu}m$이내 열간 내마모성, 크립저항성이 요구되는 경우 : 질화층 $300{\sim}400{\mu}m$ TiN, CrN 등 세라믹 코팅에 의한 성능 향상 내식성 중요시 CrN, DLC의 적용 내마모성 및 초저마찰계수의 구현 : 방향성 코팅, 나노구조화 금형의 국제경쟁력을 향상시키기 위해서는 고품위 금형 제조 기술이 필요하고 이를 위하여, 표면개질처리가 필수불가결하다는 것이다. 또한, 열 표면처리에는 각각의 특징이 있고, 적용 상황의 미묘한 차이에 따라 특성이 바뀌기 때문에 고품위, 품질 금형을 얻고자 하면 어느 때보다 사용자, 금형기술자, 열 열 표면처리 기술자들과의 협력이 요구된다.

• Journal of Korean Society of Water and Wastewater
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• v.18 no.2
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• pp.181-187
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• 2004

The purpose of this study is to investigate the biofilm reactors capable of doing high efficiency treatment. Vertical fluidized bed biofilm reactor(VFBBR) and spiral fluidized bed biofilm reactor(SFBBR) was used for their performence in biodegradation of artificial sewage. The factors influencing the efficiency of those reactors were compared with difference of physical condition. They had same size but different structure to gain access of its unique characteristics. When recycle solution with flow rate of 22 mL/min and artificial sewage with flow rate of 2~10 mL/min were fed into two reactors in aerobic state, the average $COD_{cr}$, removal rate for biodegradation of SFBBR was greater than VFBBR. After reactor feed sewage was constantly maintained as flow rate of 4 mL/min and the recycle solution were changed to 10~32 mL/min respectively, the average $COD_{cr}$ removal rate of artificial sewage in SFBBR was greater than VFBBR. In this experiment for addition of support media into two reactors SFBBR was 4.1% excellent than VFBBR. Above all, SFBBR excelled VFBBR in boidegradation of organic matter in sewage.

• Korean Journal of Materials Research
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• v.17 no.5
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• pp.256-262
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• 2007

Effects of interlayer and the combination of different coating methods on the mechanical and corrosion behaviors of TiN and CrN coated on 420 stainless steel have been studied. STS 420 specimen were tempered at $300^{\circ}C$ for 1 hr in vacuum furnace. The TiN and CrN thin film with 2 ${\mu}m$ thickness were coated by arc ion plating and DC magnetron sputtering following the formation of interlayer for pure titanium and chromium with 0.2 ${\mu}m$ thickness. The microstructure and surface analysis of the specimen were conducted by using SEM, XRD and roughness tester. Mechanical properties such as hardness and adhesion also were examined. XRD patterns of TiN thin films showed that preferred TiN (111) orientation was observed. The peaks of CrN (111) and $Cr_2N$ (300) were only observed in CrN thin films deposited by arc ion plating. Both TiN and CrN deposited by arc ion plating had the higher adhesion and hardness compared to those formed by magnetron sputtering. The specimen of TiN and CrN on which interlayer deposited by magnetron sputtering and thin film deposited by arc ion plating had the highest adhesion with 22.2 N and 19.2 N. respectively. TiN and CrN samples shown the most noble corrosion potentials when the interlayers were deposited by using magnetron sputtering and the metal nitrides were deposited by using arc ion plating. The most noble corrosion potentials of TiN and CrN were found to be approximately -170 and -70 mV， respectively.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.5
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• pp.709-716
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• 2016

Recently, the operating conditions of the various mechanical structures have become more severe and the running time has become longer as the development of plant equipment increases with the introduction of high technology. Thus, the reliability of the system and its accessories is becoming a problem. Normally, synthetic natural gas (SNG) plants use 1.25Cr-0.5Mo or 2.25Cr-1Mo heat resistant steel according to the operating conditions. In this study, a lab-scale reactor was set up using 1.25Cr-0.5Mo steel, in order to carry out corrosion tests for producing synthetic natural gas. The corrosive characteristics were investigated under 1st-methanator operating conditions and fundamental data about the durability and reliability were obtained by using the experimental test. The analysis of results obtained on the durability of the reactor under emission and injection compositions showed that the hydrogen embrittlement caused by hydrogen and the oxidation corrosion caused by H2O had the most effect on the durability of 1.25Cr-0.5Mo steel in the SNG reactor. However, the hydrogen embrittlement and oxidation corrosion occurred simultaneously under emission conditions, so that the corrosion of the material increased suddenly after a long operating time. Besides, the corrosion of the 1.25Cr-0.5Mo steel under the injection composition was faster than that under the emission composition.

• Journal of the Korean Society for Heat Treatment
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• v.22 no.5
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• pp.307-311
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• 2009

In this study, TiCrN films were deposited on STS 316 Land Si (100) wafer by inductively coupled plasma (ICP) assisted D.C. magnetron sputtering. The effect R.F. power for ICP discharge on the mechanical properties of TiCrN films was investigated. XRD, XPS and FE-SEM were used for the structure analysis. Also the Micro-Knoop hardness tester and profilometer were used for measuring hardness of coatings and film stress respectively. As increasing the R.F. power for ICP discharge, thickness of coating was decreased from 1633 nm to 1288 nm but hardness was increased about $Hk_{5g}$ 4200 at 400 W. All of the XRD patterns showed (111), (200) and (220) peaks of TiCrN films. Surface morphology was studied using the profilometer. FE-SEM was used to know morphology and cross-section of the films. Structure of the films was changed dense as increased ICP power.

• Korean Journal of Materials Research
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• v.10 no.7
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• pp.505-514
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• 2000

The carburizing behavior and fatigue properties of the plasma carburized low carbon Cr-Mo steel(0.176C-1.014Cr-0.387Mo) have been investigated. The effective case depth in plasma carburized steel increased up to 50% in comparison with that of gas carburizing, and this case depth increased with the increasing surface carbon content. With increasing time in plasma carburizing, the surface carbon content increased but its increasing rate decreased. Fatigue properties were studied in terms of microstructure, case depth, retained austenite and residual stress near the surface. The fatigue limit of the plasma carburized steel was higher than that of gas carburized one. The initiation of microcracks and initial crack propagation were retarded due to a relatively little surface and internal oxidation layer in plasma carburized steel. Fractography showed the crack initiated at the surface, and transgranular fracture at surface layer was more predominant in plasma carburized steel compared to that of gas carburized steel.

• Corrosion Science and Technology
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• v.11 no.6
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• pp.263-269
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• 2012

Copper alloys are commonly applied to ship's propellers, pumps and valves which are serviced in seawater due to their good castability and corrosion resistance. In the environment of high flow velocity, however, erosion damage predominates over corrosion damage. In particular, the cavitation in seawater environment accelerates surface damage to copper alloys, resulting in degradation of products and economic losses and also threatening safety. The surface was coated with WC-27NiCr by high velocity oxygen fuel(HVOF) spraying technique to attain durability and cavitation resistance of copper alloys under high velocity/pressure flow. The cavitation test was performed for the WC-27NiCr coating deposited by HVOF in seawater at the amplitude of $30{\mu}m$ with seawater temperature. The cavitation at $15^{\circ}C$ caused exfoliation of the coating layer in 17.5 hours while that of $25^{\circ}C$ caused the exfoliation in 12.5 hours. When the temperature of seawater was elevated to $25^{\circ}C$ from $15^{\circ}C$, more damage was induced by over 160%. Although WC-27NiCr has good durability, corrosion resistance and eletrochemical stability, the cavitation damage rate of the coating layer could remarkably increase at the elevated temperatures under cavitation environments.

• Journal of the Korean Ceramic Society
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• v.39 no.2
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• pp.171-177
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• 2002

In this study, the vertical aligned carbon nanotubes was synthesized by DC bias-assisted Inductively Coupled Plasma Hot-Filament Chemical Vapor Deposition (ICPHFCVD). The substrate used CNTs growth was Ni(300 ${\AA}$)/Cr(200 ${\AA}$)-deposited one on glass by RF magnetron sputtering. R-F, DC bias and filament power during the growth process were 150 W, 80 W, 7∼8 A, respectively. The grown CNTs showed hollow structure and multi-wall CNTs. The top of grown CNT was found to Ni-tip that the CNT end showed to metaltip. The graphitization and field emission properties of grown was better than grown CNTs by ICPCVD. The turn-on voltage of CNT grown by DC bias-assisted ICPHFCVD showed about 3 V/${\mu}m$.

• Transactions of the Korean hydrogen and new energy society
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• v.20 no.6
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• pp.455-463
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• 2009

코발트 보호막 코팅이 적용된 페라이트계 스테인리스 스틸인 STS 430과 STS 444 소재에 대해 고체산화물 연료전지용 금속연결재로서의 고온 산화 특성에 대해 살펴보았다. 코발트 코팅층은 $800^{\circ}C$ 고온 산화 후 코발트 산화물 및 $Co_2CrO_4$, $CoCr_2O_4$, $CoCrFeO_4$ 등과 같은 코발트가 함유된 스피넬 상을 형성하였다. 또한 페라이트계 스테인리스 스틸과 코발트 코팅의 계면에서 크롬과 철이 함유된 치밀한 산화층을 형성하여 금속연결재 표면의 스케일 성장속도를 감소시키고 금속연결재 내에 함유된 크롬의 외부 확산을 효과적으로 억제하였다. 한편 STS 430은 고온 산화 후 표면에 형성된 스케일 하부에 $SiO_2$와 같은 내부 산화물이 형성된 반면 STS 444는 표면 스케일 이외에 다른 내부 산화물은 확인되지 않았으며 고온에서의 면저항 측정 결과, 코발트가 코팅된 STS 444의 전기 전도성이 STS 430 보다 우수한 것으로 나타났다.