• Horticultural Science & Technology
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• v.18 no.4
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• pp.529-535
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• 2000

Organic materials such as composted rice-hull, saw dust, and pine bark, and inorganic materials such as vermiculite, perlite, and recycled rockwool were commonly employed as container media in domestic greenhouse industry. The objective of this research was to get informations in soil physico chemical properties of those materials. Composted dry-peeling bark and wet-peeling bark had 72.1% and 69.1%, respectively, in particles larger than 1.0 mm, which were much higher than 34.7% of composted rice-hull and 33.7% of composted saw dust. Imported vermiculite had 89.9%, but domestic vermiculite had 25.7% in particles larger than 1 mm. In soil physical properties, Russian peat had the highest container capacity of 79.3%, and wet-peeling bark had the lowest container capacity of 58.2%. However, Russian peat and composted saw-dust had 4.1% in air space indicating that possible problems could occur in soil aeration when those are employed for container grown crops. Saw dust had $2.3mS{\cdot}cm^{-1}$ in electrical conductivity, while other composted organic materials had less than $0.25mS{\cdot}cm^{-1}$. Imported vermiculite had 64.0 meq/100 g in cation exchange capacity, which was 2.4 times higher than those of domestic vermiculite, 27.2 meq/100 g. Domestic vermiculite had higher Ca and Mg and less Na contents than those of imported vermiculite.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2018.06a
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• pp.109-109
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• 2018

Cr-Mo 합금강은 고온 환경 하에서 높은 크리이프 강도와 우수한 내식성 때문에 발전설비, 석유 화학, 그리고 해양산업과 같은 여러 산업분야에서 널리 사용되고 있다. 특히, Cr-Mo 강의 내식성은 합금 내 Cr 함량에 크게 의존한다. 이는 고온에서 Cr과 O가 화학적 반응을 일으킴에 따라 보호성의 Cr 산화스케일을 형성하기 때문이다. 그러나 화석연료를 사용하는 발전설비의 경우, $SO_2$가 포함된 강한 부식성의 연소 가스가 배출되며, 이에 노출된 금속의 표면에서는 산화와 황화가 동시에 발생한다. 황화스케일은 산화스케일에 비해 매우 빠르게 성장하며, 그 특성이 매우 취약하기 때문에 황화 환경에서 금속의 내식성 및 기계적 물성치는 보다 크게 저하된다. 따라서 본 연구에서는 화력 발전소의 증기발생용 튜브 재료인 9Cr-1MoVNb 강을 선정하였으며, $SO_2$ 가스 환경 하에서의 부식 및 기계적 물성치 저하 특성을 평가하고자 하였다. 본 연구에서 사용된 9Cr-1MoVNb강의 화학 성분 조성은 0.1 C, 0.38 Si, 0.46 Mn, 0.25 Ni, 8.38 Cr, 0.93 Mo, 0.18 V, 0.09 Nb, 그리고 나머지는 Fe이다. 부식시험은 가공된 미소시험편과 인장시험편을 전기열처리로에 장입한 후, $650^{\circ}C$에서 $N_2+O_2+O_2+SO_2$ 조성의 가스를 분당 50 CC로 흘려주었다. 제작된 시험편에 대한 부식거동은 무게 증가량, optical microscope, scanning electron microsope, 그리고 energy dispersive x-ray spectrum을 통해 평가하였다. 그리고 기계적 물성치 평가를 위한 인장시험은 분당 2mm 변위제어를 통해 실시하였다. 그 결과, 9Cr-1MoVNb 강은 $SO_2$ 가스 환경 하에서 비 보호적인 Fe-풍부상의 산화 스케일층이 두껍게 형성됨에 따라 열악한 내식성을 나타냈다. 그에 따라 기계적 물성치는 저하되는 경향을 나타내었다.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2015.11a
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• pp.256-257
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• 2015

마그네슘 합금은 낮은 비중, 높은 비강도, 주조성 및 절삭가공성, 치수안정성, 내흠집성이 우수한 특성을 지니고 있는 경량금속으로써 우수한 주조성과 상온강도, 연신율을 나타낸다. 최근에는 마그네슘 합금을 사용한 IT 기기의 케이스 및 자동차 내, 외장 부품 등의 제품이 다양하게 출시되어지며 금속 질감의 감성 기능까지 적용시킨 전자 기기 제품에 대한 수요가 급증하고 있는 추세이다. 하지만 마그네슘 합금의 낮은 부식 저항성은 마그네슘 합금을 적용시킨 제품에 큰 단점으로 작용되고 있으며 이를 해결하기 위한 연구가 활발히 진행 중이다. 본 연구에서는 플라즈마 전해산화법과 실리카 졸-겔 코팅법을 이용하여 마그네슘 합금의 내부식성을 향상시킴과 동시에 금속질감의 감성 기능을 구현하고자 하였다. 플라즈마 전해산화 공정으로 형성된 산화피막층과 $SiO_2$ 코팅으로 형성된 코팅층의 표면과 단면에 대해서는 FE-SEM(Field emission Scanning Electron Microscope)과 FE-TEM(Field emission Transmission Electron Microscope)으로써 확인하였고 전기화학적 특성 분석을 통한 동전위(Potentiodynamic polarization)와 EIS(Eletrochemical Impedance Spectroscopy) 그리고 Salt spray등을 분석하였다.

• Corrosion Science and Technology
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• v.17 no.4
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• pp.166-175
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• 2018

In this study, the electrochemical properties of CP-Ti (commercially pure titanium) and Ti-64 (Ti-6Al-4V) were evaluated and the effect of hydrofluoric acid on corrosion resistance and electrochemical properties was elucidated. Additive manufactured materials were made by DMT (Directed Metal Tooling) method. Samples were heat-treated for 1 hour at $760^{\circ}C$ and then air cooled. Surface morphologies were studied by optical microscope and SEM. Electrochemical properties were evaluated by anodic polarization method and AC-impedance measurement. The oxide film formed on the surface was analyzed using an XPS. The addition of HF led to an increase in the passive current density and critical current density and decreased the polarization resistance regardless of the alloys employed. Based on the composition of the oxide film, the compositional difference observed by the addition of HF was little, regardless of the nature of alloys. The Warburg impedance obtained by AC-impedance measurement indicates the dissolution of the constituents of CP-Ti and Ti-64 through a porous oxide film.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2005.05a
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• pp.389-394
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• 2005

Microfactory is effective method for machining micro size component. Electro-chemical machining can be more suitable to a microfactory than other machining methods in terms of maintaining high accuracy. Surface profile of EDM Machined component is predicted by micro EDM simulation using superpositioning spark crater. Planar motor and micro pump are developed to construct microfactory system.

• Corrosion Science and Technology
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• v.17 no.6
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• pp.310-316
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• 2018

The effect of passive film on corrosion of metals and alloys in a static corrosive environment has been studied by many researchers and is well known, however few studies have been conducted on the electrochemical measurement of metals and alloys during cavitation corrosion conditions, and there are no test standards for electrochemical measurements 'During cavitation' conditions. This study used commercially additive manufactured(AM) pure titanium in tests of anodic polarization, corrosion potential measurements, AC impedance measurements, and repassivation. Tests were performed in 3.5% NaCl solution under three conditions, 'No cavitation', 'After cavitation', and 'During cavitation' condition. When cavitation corrosion occurred, the passive current density was greatly increased, the corrosion potential largely lowered, and the passive film revealed a small polarization resistance. The current fluctuation by the passivation and repassivation phenomena was measured first, and this behavior was repeatedly generated at a very high speed. The electrochemical corrosion mechanism that occurred during cavitation corrosion was based on result of the electrochemical properties 'No cavitation', 'After cavitation', and 'During cavitation' conditions.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2018.06a
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• pp.110-110
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• 2018

여러 니켈합금 중 인코넬 600은 원전 가압경수로(PWR)의 튜브 재료로 널리 사용되는 재료이다. 스테인리스강과 비교하여 우수한 내식성과 기계적 특성으로 인해 화학설비, 발전설비, 그리고 해양설비 등과 같은 여러 산업분야에서도 널리 사용되고 있다. 그러나 가압경수로용 증기 발생기의 튜브 재료와 같은 특수 환경에서 예민화에 따른 입계부식 및 입계응력부식 등의 문제가 흔히 보고되고 있다. 이러한 내구성 문제는 설비 및 장비의 수명, 내구성 그리고 안정성 등의 치명적인 영향을 미친다. 따라서 용접, 열처리, 그리고 가공과정에서 발생하는 Inconel 600의 예민화 및 입계부식에 관한 연구가 활발히 진행되고 있다. 그러나 100시간 이상 장시간 열화된 시편에 대한 예민화 연구는 전무한 실정이다. 본 연구에서는 장시간 열화된 Inconel 600의 예민화를 평가하기 위해 최대 1,000시간까지 열화를 실시하였으며, 이에 대한 평가방법으로 Double-Loop Electrochemical Potentiokinetic Reactivation(DL-EPR) 시험법을 적용하였다. 본 실험에서 사용된 인코넬 600의 화학성분(wt, %)은 0.01 C, 0.05 Si, 0.14 Mn, 15.3 Cr, 0.5 Cu, 0.015 S, 그리고 나머지는 Ni 이다. 예민화 평가를 위한 등온 열화는 전기열처리로를 이용하여, $550^{\circ}C$와 $650^{\circ}C$에서 최대 1000시간까지 실시하였다. 열화에 따른 미세조직 변화는 scanning electron microscope와 energy dispersive x-ray spectroscopy를 이용하여 실시하였다. DL-EPR 실험은 $25^{\circ}C$의 0.1M $H_2SO_4$ + 0.001M KSCN(potasium thiocyanate) 수용액 하에서 실시하였으며, 분극은 OCP로부터 600 mV(SSE vs.)까지 1.67mV/s 주사속도로 forward scan을 실시 후, 동일한 속도로 OCP까지 reverse scan을 실시하였다. Degree Of Sensitization(DOS)값은 anodic scan peak($I_a$) 값과 reverse scan peak($I_r$) 값의 비로 산출하였다. $$i.e.\;DOS=I_r/I_a{\times}100$$. 그 결과, 온도 변수에 따른 Inconel 600강의 예민화 거동은 서로 상이한 경향을 나타내었다. $550^{\circ}C$의 경우, 열화가 진행됨에 따라 DOS값은 급격하게 증가하는 경향을 나타냈다. 반면, $650^{\circ}C$에서는 일정시간 이후부터 Cr 확산 현상에 의한 탈 예민화 현상이 관찰되었다.

• Journal of the Korea Concrete Institute
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• v.21 no.3
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• pp.367-375
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• 2009

Recently, more focus is shift to imbalances in aggregate market supply and demand and an exhaustion of natural resources. In this situation, Electric arc furnace oxidizing slag (EAF slag) has high application possibility as aggregate for concrete due to similar property with general aggregate. However, it is inherent the problem which causes pop-out by free-CaO contained in slag In this study, we've got the plan to assure the chemical stability of EAF slag, and then experimentally tested the mechanical performance and durability for the fine aggregate used EAF slag. On this test result, we suggest the application plan. At the result of this study, it shows that EAF slag would reduce the surface defect such as pop-out due to natural aging for the fixed hour and adjustment the grain size of EAF slag. And mechanical performance and durability according to the replacement rate of concrete service, were revealed more than equal or equal compare to general aggregate. Hereafter, quality control must precede not to impede the beauty of concrete surface as assure the safety for aging and processing. And, to establish the environmental resource recycling system for by-products of steel, it should be made development of various application and guideline of quality control for the EAF slag aggregate. Moreover, it must be constantly studied all kind of engineering performance and durability for related to this study.

• Journal of the Korea institute for structural maintenance and inspection
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• v.18 no.3
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• pp.133-142
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• 2014

Recently, more focus is shift to imbalances in aggregate market supply and demand and an exhaustion of natural resources. In this situation, Electric arc furnace oxidizing slag (EAF Slag) has high application possibility as aggregate for concrete due to similar property with general aggregate. In this study, We've got the plan to assure the chemical stability of EAF Slag, and then experimentally tested the mechanical performance and durability for the fine aggregate used EAF Slag. On this test result, we suggest the application plan. At the result of this study, it shows that EAF slag would reduce the surface defect such as pop-out due to natural aging for the fixed hour and adjustment the grain size of EAF Slag. And mechanical performance and durability according to the replacement rate of concrete service, were revealed more than equal or equal compare to general aggregate. Hereafter, quality control must precede not to impede the beauty of concrete surface as assure the safety for aging and processing. And, to establish the environmental resource recycling system for by-products of steel, it should be made development of various application and guideline of quality control for the EAF slag aggregate. Moreover, it must be constantly studied all kind of engineering performance and durability for related to this study.

• Polymer(Korea)
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• v.32 no.5
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• pp.458-464
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• 2008

A successful scaffold should have a highly porous structure and good mechanical stability. High porosity and appropriate pore size provide structural matrix for initial cell attachment and proliferation enabling the exchange of nutrients between the scaffold and environment. In this paper the highly porous scaffold of poly(${\varepsilon}$-caprolactone) electrospun nanofibers could be manufactured with an auxiliary electrode and chemical blowing agent (BA) under several processing conditions, such as the concentration of PCL solution, weight percent of a chemical blowing agent, and decomposition time of a chemical blowing agent. To attain stable electrospinnability and blown nanofiber mats having high microporosity and large pore, a processing condition, 8wt% of PCL solution and 0.5wt% of a chemical blowing agent under $100^{\circ}C$ and decomposition time of $2{\sim}3\;s$, was used. The growth characteristic of human dermal fibroblasts cells cultured in the mats showed the good adhesion and proliferation on the blown mat compared to a normal electrospun mat.