• 플랜트 저널
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• 제6권2호
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• pp.70-77
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• 2010

This study investigated the characteristics of co-combustion of mixed anthracite (domestic and Vietnam) and bituminous coal (Sonoma, Australia) at circulating fluidized bed boiler in Donghae thermal power plant when mixing ratio of bituminous coal is variable. Co-combustion of bituminous coal contributes to improvement in general combustion characteristics such as moderately retaining temperature of furnace and recycle loop, reducing unburned carbon powder, and reducing discharge concentration of NOx and limestone supply owing to improvement in anthracite combustibility as the mixing ratio was increased. However, bed materials were needed to be added externally when the mixing ratio exceeded 40% because of reduction in generating bed materials based on reduction in ash production. When co-combustion was conducted in the section of 40 to 60% in the mixing ratio while the supplied particles of bituminous coal was increased from 6 mm to 10 mm, continuous operation was shown to be possible with upper differential pressure of 100 mmH2O (0.98 kPa) and more without addition of bed materials for the co-combustion of mixed anthracite and bituminous coal (to 50% or less of the ratio) and that of domestic coal and bituminous coal (to 60% of the ratio).

• 한국결정성장학회지
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• 제25권1호
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• pp.6-12
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• 2015

율속제어소결은 소결 공정 중 실시간으로 측정되는 시편의 팽창/수축거동을 이용해 일정한 수축거동을 하도록 로의 파워를 조정하는 소결방법으로, 온도를 조절하기 위해 로의 파워를 제어하는 일반적인 소결에 비해 시편의 소결 과정을 세밀히 제어할 수 있으며, 특히 소결공정의 최적화를 이룰 수 있는 장점이 있다. 본 연구에서는 탄화붕소의 소결에 율속 제어소결을 적용해 각 공정변수의 조절에 따른 소결온도 및 입자성장의 변화를 조사하여 그 상관관계를 규명하고 이를 기존의 이론에 맞추어 해석함으로써 율속제어소결을 어떻게 소결공정 최적화에 이용할 수 있는지 그 가능성을 알아보았으며 이를 통해 향후 미지 소재의 소결공정에 율속제어공정을 어떻게 적용할 수 있는지 고찰해 보았다.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2005년도 춘계학술대회 논문집 디스플레이 광소자 분야
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• pp.76-79
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• 2005

$Nd:YVO_4$ 연속발진 레이저(CW laser:Continuous wave laser)로 제작한 다결정 실리콘 박막의 이온도핑 효과를 조사하였다. PECVD로 증착한 비정질 실리콘 박막을 CW 레이저를 조사하여 결정화한 후 $B_2H_6$ 플라즈마 이온 도즈량을 변화시켜 이온 도핑을 하고 급속열처리 방법과 퍼니스 어닐링 방법으로 도펀트 활성화를 하였다. 이온 도핑된 CW 다결정 실리콘 박막의 이온 도즈량에 따른 판저항 변화를 비교하고, 급속열처리(RTA: Rapid Thermal Annealing)와 퍼니스 어닐링(FA: Furnace Annealing) 전후의 결정성 변화를 라만 스펙트럼(Raman spectrum) 을 통하여 분석하였다. 이온 도즈량이 증가함에 따라 판저항은 감소하고, 어닐링 후 이온 도핑에 의해 손상된 박막이 복원됨을 확인 할 수 있다.

• 한국수소및신에너지학회논문집
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• 제30권2호
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• pp.111-118
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• 2019

Greenhouse gas emissions have a profound effect on global warming. Various environmental regulations have been introduced to reduce the emissions. The largest amount of greenhouse gases, including carbon dioxide, is produced in the steel industry. To decrease carbon dioxide emission, hydrogen-based iron oxide reduction, which can replace carbon-based reduction has received a great attention. Iron production generates various by-product gases, such as cokes oven gas (COG), blast furnace gas (BFG), and Linz-Donawitz gas (LDG). In particular, COG, due to its high concentrations of hydrogen and methane, can be reformed to become a major source of hydrogen for reducing iron oxide. Nevertheless, continuous COG cannot be supplied under actual operation condition of steel industry. To solve this problem, this study proposed to use two alternative COG-based fuel mixtures; one with natural gas and the other with biogas. Reforming study on two types of mixed gas were carried out to evaluate catalyst performance under a variety of operating conditions. In addition, methane conversion and product composition were investigated both theoretically and experimentally.

• 콘크리트학회논문집
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• 제27권3호
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• pp.237-244
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• 2015

시멘트는 건설 산업의 발전과 비례하여 눈부신 발전을 이루었다. 그러나 이산화탄소의 발생량 또한 매우 치명적이다. 이러한 문제를 해결하기 위해 이산화탄소의 배출이 적은 시멘트의 개발이 시급한 상황이다. 따라서 본 연구에서는 시멘트의 대체제로 소성과정이 없어 에너지 손실률이 낮으며 이산화탄소의 배출량이 적은 비소성 시멘트(Non-Sintered Cement, 이하 NSC) 모르타르를 개발하고자 하였다. 산업 부산물인 고로슬래그 미분말(Granulated ground Blast Furnace Slag, 이하 GBFS)에 이를 활성화시키기 위한 자극제를 배합하였다. 그리고 GBFS와 자극제의 배합비율이 어떠한 양생조건에서 우수한 지를 알아보기 위해 각각의 양생조건에 따른 휨 및 압축강도, 그에 따른 수화 반응 생성물과 메커니즘을 알아보기 위해 SEM, XRD 실험을 진행하였고, 또한 화학저항성, pH측정, 염화물 이온 침투 저항성 및 탄산화 촉진실험을 실시하여 내구성을 알아보았다. 실험 결과 보통 포틀랜드 시멘트와 비교하여 전체적으로 우수한 특성과 내구성을 보여주었고, 콘크리트 2차 제품으로 개발하여 경제성 향상, 친환경적인 제품 생산, 환경문제 및 에너지 절약에 큰 이바지를 할 것으로 기대된다.

• Corrosion Science and Technology
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• 제8권2호
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• pp.74-80
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• 2009

The high alkaline property in the concrete pore solution protects the embedded steel in concrete from corrosion due to aggressive ions attack. However, a continuous supply of those ions, in particular, chlorides altogether with a pH fall in electrochemical reaction on the steel surface eventually depassivate the steel to corrode. To mitigate chloride-induced corrosion in concrete structures, finely grained mineral admixtures, for example, pulverized fuel ash (PFA), ground granulated blast furnace slag (GGBS) and silica fume (SF) have been often advised to replace ordinary Portland cement (OPC) partially as binder. A consistent assessment of those partial replacements has been rarely performed with respect to the resistance of each binder to corrosion, although the studies for each binder were extensively looked into in a way of measuring the corrosion rate, influence of microstructure or chemistry of chlorides ions with cement hydrations. The paper studies the behavior of steel corrosion, chloride transport, pore structure and buffering capacity of those cementitious binders. The corrosion rate of steel in mortars of OPC, 30% PFA, 60% GGBS and 10% SF respectively, with chloride in cast ranging from 0.0 to 3.0% by weight of binder was measured at 7, 28 and 150 days to determine the chloride threshold level and the rate of corrosion propagation, using the anodic polarization technique. Mercury intrusion porosimetry was also applied to cement pastes of each binder at 7 and 28 days to ensure the development of pore structure. Finally, the release rate of bound chlorides (i.e. buffering capacity) was measured at 150 days. The chloride threshold level was determined assuming that the corrosion rate is beyond 1-2 mA/$m^3$ at corrosion and the order of the level was OPC > 10% SF > 60% GGBS > 30% PFA. Mercury intrusion porosimetry showed that 10% SF paste produced the most dense pore structure, followed by 60% GGBS, 30% PFA and OPC pastes, respectively. It was found that OPC itself is beneficial in resisting to corrosion initiation, but use of pozzolanic materials as binders shows more resistance to chloride transport into concrete, thus delay the onset of corrosion.

• 비파괴검사학회지
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• 제34권3호
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• pp.241-247
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• 2014

본 연구는 고온강도와 화학적 안전성으로 산업기계 구조물의 주요 소재로 사용되고 있는 AISI316 오스테나이트기 스테인레스강의 장시간 등온열처리에 따른 초음파 비선형성 특성을 평가하였다. 장시간 등온열처리는 정해진 시간을 변수로 전기로에서 가속열처리를 수행하였다. 미세조직적으로 정밀분성을 통하여 장시간 열처리에 따른 초음파 비선형성의 변화와 미시적 손상거동을 면밀히 평가하였다. 초음파 비선형성은 1000시간까지 급격하게 감소하고 이후 서서히 감소하였다. 표면조직적으로 입계의 모양이 다각형에서 원형으로 변하며 특히, 1000시간에서는 쌍정이 모두 분해되었다. 입계에 존재하던 델타페라이트는 1000시간에서 관찰되지 않으며 ${\sigma}$상으로 지속적인 변태가 진행되었다. 결과적으로 열처리 초기에는 보이드나 전위의 소멸 그리고 쌍정의 소멸로 초음파 비선형성은 급격히 감소를 하고 이후에는 입계에 $Cr_{23}C_6$석출물의 생성과 ${\sigma}$상 생성으로 초음파 비선형성은 미소하지만 지속적으로 감소한 것으로 판단된다.

• Journal of Biosystems Engineering
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• 제31권1호
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• pp.33-38
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• 2006

This work was conducted to find the operating characteristics of an efficient wet grinding system designed to obtain fine rice husk ash powder. Once the rice husk was combusted and the thermal energy was recovered from the furnace, the ash was fed and pulverized in the grinding system resulting a fine powder to be used as a supplementary adding material to the portland cement. Grinding time (15, 30, 45 min), impeller speed (250, 500, 750 rpm), and mixed ratio (6.7, 8.4, 11.l, 20.9) were three operating factors examined for the performance of a wet-type stirred ball mill grinding system. For the operating conditions employed, mean diameter of fine ash powder, specific energy input, and grinding energy efficiency were in the range of $2.83{\sim}9.58{\mu}m,\;0.5{\sim}6.73kWh/kg,\;and\;0.51{\sim}3.27m^2/Wh$, respectively. With the wet-type stirred ball mill grinding system used in this study, the grinding energy efficiency decreased with the increase in total grinding time, impeller speed, and mixed ratio. The difference in specific surface area of powder linearly increased with logarithm in total number of impeller revolution and the grinding energy efficiency linearly decreased. Grinding time of 45 min, impeller speed of 500 rpm, and mixed ratio of 6.7 were chosen as the best operating condition. At this condition, mean particle diameter of the fine ash, grinding energy efficiency, grinding throughput, and specific energy input were $2.84{\mu}m,\;2.28m^2/Wh,\;0.17kg/h$, and 2.03kWh/kg, respectively. Wet fine grinding which generates no fly dust causing pollution and makes continuous operation easy, is appeared to be a promising solution to the automatization of rice husk ash grinding process.

• 한국주조공학회지
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• 제21권4호
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• pp.253-259
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• 2001

There are many methods to produce metal foams, which can be classified into three groups according to the state of the starting metal i.e. liquid or powder or solid. Three types of defects such as cell closing, cell deformation or breakdown and cell misrun are thought to be occurred when we make the open cell aluminum foams by precision casting. Filling ability of the mold slurry between preform is related with cell closing, mold collapsibility is related with cell deformation or breakdown, mold temperature and pouring pressure are related with cell misrun. These factors can be evaluated by measuring slurry fluidity, burnout strength and permeability of the mold. Properties of the plaster mold were evaluated to find optimum mold conditions for high quality open cell aluminum foam in this study. Permeability was almost zero independent of burnout conditions, however, crack initiation was found on the surface of all specimens one or two minutes after taking out from the furnace. Crack has grown and disappeared with time. This crack may facilitate the mold filling when molten metal is poured, because of the improved mold permeability. It was considered that crack initiation and disappearance was closely related with temperature difference between the surface and inner part. Knocking-out the mold is a difficult problem due to the small cell size, because continuous mesh structure of the metal foam is not strong. It is not easy to remove molding material after pouring. We can expect that water quenching can facilitate the knocking-out the mold after solidification without damaging cell structures. Collapsed particles after water quenching became bigger with the increase in time.

• 한국분말재료학회지
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• 제18권5호
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• pp.430-436
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• 2011

Joining of NiO-YSZ to 316 stainless steel was carried out with B-Ni2 brazing alloy (3 wt% Fe, 4.5 wt% Si, 3.2 wt% B, 7 wt% Cr, Ni-balance, m.p. 971-$999^{\circ}C$) to seal the NiO-YSZ anode/316 stainless steel interconnect structure in a SOFC. In the present research, interfacial (chemical) reactions during brazing at the NiO-YSZ/316 stainless steel interconnect were enhanced by the two processing methods, a) addition of an electroless nickel plate to NiO-YSZ as a coating or b) deposition of titanium layer onto NiO-YSZ by magnetron plasma sputtering method, with process variables and procedures optimized during the pre-processing. Brazing was performed in a cold-wall vacuum furnace at $1080^{\circ}C$. Post-brazing interfacial morphologies between NiO-YSZ and 316 stainless steel were examined by SEM and EDS methods. The results indicate that B-Ni2 brazing filler alloy was fused fully during brazing and continuous interfacial layer formation depended on the method of pre-coating NiO-YSZ. The inter-diffusion of elements was promoted by titanium-deposition: the diffusion reaction thickness of the interfacial area was reduced to less than 5 ${\mu}m$ compared to 100 ${\mu}m$ for electroless nickel-deposited NiO-YSZ cermet.