수용액내에서 Mg/Al-NO3 및 Ca/Al-NO3 층상이중수산화물(LDHs)의 염소이온 고정화 특성에 관한 실험적 연구

Abstract

국문요지

콘크리트의 내구성능을 저하시키는 다양한 유해이온 중 염소이온(Cl-)은 염해열화작용의 가장 큰 요인이다. 지속적으로 염소이온이 침투하여 부동태 피막의 약점에 흡착하게 되고 피막을 국부적으로 파괴하므로 철근부식이 급속히 진행된다. 기존 염해열화 억제 방법은 폴리우레탄, 에폭시와 같은 유기계 마감재의 사용과 낮은 물시멘트비를 사용하거나 실리카흄을 사용하는 시멘트 마감재, 에폭시 도막 철근의 사용, 실링재 충진, 방청제 사용 등이 있지만 기존의 염소이온 억제 방법들은 주로 수동적이며, 염소이온에 대한 선택성 부족, 평가적 성격으로 대책에 대한 명확한 방법론은 제시되지 못하고 있다고 판단된다. 최근에는 국외를 위주로 유해이온을 제거하는 새로운 재료들이 개발되고 있다. 그 중 음이온성 점토물질의 일종인 층상이중수산화물(Layered Double Hydroxides)이 다양한 분야에서 응용되어지고 있으며, 산업계 및 학계에서 많은 주목을 받고 있다. 국내의 경우 수질, 토질, 대기분야에서의 유해이온을 제거하는 연구가 주를 이루고 있으며, 건축분야에서의 염소이온과 같은 유해이온을 사전에 차단하기 위한 제거방법이나 고정화 방법에 관한 연구는 전무한 실정이다. 따라서 본 연구는 두 종류의 층상이중수산화물을 직접 합성 제조하여 구조적 특성을 고찰하고 최종단계인 콘크리트 레벨의 기초적 자료를 마련하기 위하여 두 종류의 LDHs를 혼입하고 수용액 레벨에서의 염소이온 고정효율을 평가하였다.

본 실험결과 기존문헌과의 LDHs와 본 연구에서 직접 제조한 LDHs의 XRD 패턴비교 결과 매우 유사하였고, 합성이 양호하게 되었음을 알 수 있었다. 또한, SEM분석 결과를 통해 Ca/Al-NO3 체계는 Mg/Al-NO3 체계보다 뚜렷한 판각구조의 육각형 형태로 관찰되었으며, 결정의 크기는 Ca/Al-NO3 체계의 경우 약 20~30 ㎛, Mg/Al-NO3 체계는 약 300~500 ㎚정도로 관찰되었다. 염소이온 고정효율 평가 실험 결과는 Ca/Al-NO3 체계와 Mg/Al-NO3 체계 모두 혼입량이 증가할수록 잔류 염소이온량이 감소하였으며, 이온교환 15분 이후에서의 이온고정량의 감소는 Ca/Al-NO3 체계가 우수했다. 이는 Ca/Al-NO3 체계가 염소이온과의 이온교환친화도가 높기 때문에 나타난 결과로 사료된다. 염소이온 고정효율이 우수했던 Ca/Al-NO3 체계의 LDHs를 XRD 분석한 후 이온교환 전후를 비교한 결과 층간에 삽입한 NO3가 용출되고 염소이온이 이온교환되어 치환되었음을 알 수 있었다. 또한, LDHs의 층간이 염소이온으로 이온교환되면서 면간 간격이 감소하였음을 알 수 있었다. 이는 NO3-의 반지름 크기가 0.200 ㎚인 반면에 Cl-의 반지름은 0.168 ㎚의 크기로 작은 반지름을 갖고 있기 때문이라고 사료된다.

공침법을 활용한 간단한 제조방법으로 대량생산이 가능하다고 판단되며, 시멘트계 염소이온을 고정화하는 것이 가능하다고 사료된다. 추후 시멘트계 적용 실험을 통해 검증 및 평가가 필요하다고 판단되었다.|ABSTRACT

An Experimental Study on the Properties of Chloride Binding of Mg/Al-NO3 and Ca/Al-NO3 Layered Double Hydroxides in Solution

Lee, Seung Yeop Dept. of Architetural Engineering The Graduate School Hanyang University

Cl ion, one of various ions reducing durability performance of concrete, is the most important factor in chloride attack. Cl ion continuously infiltrate concrete inside and absorb the week point of passive film. It results in the corrosion of steel bar due to the damage of passive film. Existing methods to deter chloride attack deterioration are polyurethane, the use of organic corrosion inhibitor, low W/C, cement finishing materials, epoxy-coated reinforcing bars, filling sealant and the use of rust. However it is concluded that existing methods for detering Cl are passive, lack of the selectivity of Cl ion, also clear methodology is not presented. Recently, new materials eliminating harmful ions have been developed around the world. Among them, Layered Double Hydroxides(LDH), which is one of the clay materials, has been applied in many area. There are many domestic researches on eliminating harmful ions in the area of water and soil quality and air. However there is no research or immobilization method on removing harmful ions in advance such as Cl ion in architecture area. Therefore, in this study, two types of LDHs were synthesized in person and their contextural properties were considered to capture Cl ion. In oder to obtain basic data of concrete level as final stage, two types of LDHs were mixed and Cl ion capture efficiency in aqueous solution was assessed. Based on this experimental results, there are similarities in LDHs between this experiment and literature reviews and it is concluded that the synthesis was fine. Also, through SEM analysis, Ca/Al-NO3 LDHs showed more obvious tabular structure than Mg/Al-NO3 LDHs. The crystal size of Ca/Al-NO3 LDHs was 20~30 ㎛ and the size of Mg/Al-NO3 LDHs was 300~500 ㎚ through SEM analysis. The experimental results of capture efficiency of Cl was when the amount of mixing of two types of LDHs, residual chlorine ions reduced. After 15 mins of ions exchange, the reduction of the amount of ion capture was better when Ca/Al-NO3 LDHs was used. This is because Ca/Al-NO3 LDHs has high the ability of ions exchange affinity. it is identified that interplanar spacing reduced due to the fact that interlayer was exchanged by Cl ion. This is because the radius of NO3 ion in interlayer was only 0.200 ㎚, but the radius of Cl ion was 0.168 ㎚ after ion exchange. It is concluded that LDHs can be producted massively by using co-precipitation, they are able to capture Cl ion. Through later experiment applying to cementitious materials , it should be identified and accessed.; ABSTRACT

An Experimental Study on the Properties of Chloride Binding of Mg/Al-NO3 and Ca/Al-NO3 Layered Double Hydroxides in Solution

Lee, Seung Yeop Dept. of Architetural Engineering The Graduate School Hanyang University

Cl ion, one of various ions reducing durability performance of concrete, is the most important factor in chloride attack. Cl ion continuously infiltrate concrete inside and absorb the week point of passive film. It results in the corrosion of steel bar due to the damage of passive film. Existing methods to deter chloride attack deterioration are polyurethane, the use of organic corrosion inhibitor, low W/C, cement finishing materials, epoxy-coated reinforcing bars, filling sealant and the use of rust. However it is concluded that existing methods for detering Cl are passive, lack of the selectivity of Cl ion, also clear methodology is not presented. Recently, new materials eliminating harmful ions have been developed around the world. Among them, Layered Double Hydroxides(LDH), which is one of the clay materials, has been applied in many area. There are many domestic researches on eliminating harmful ions in the area of water and soil quality and air. However there is no research or immobilization method on removing harmful ions in advance such as Cl ion in architecture area. Therefore, in this study, two types of LDHs were synthesized in person and their contextural properties were considered to capture Cl ion. In oder to obtain basic data of concrete level as final stage, two types of LDHs were mixed and Cl ion capture efficiency in aqueous solution was assessed. Based on this experimental results, there are similarities in LDHs between this experiment and literature reviews and it is concluded that the synthesis was fine. Also, through SEM analysis, Ca/Al-NO3 LDHs showed more obvious tabular structure than Mg/Al-NO3 LDHs. The crystal size of Ca/Al-NO3 LDHs was 20~30 ㎛ and the size of Mg/Al-NO3 LDHs was 300~500 ㎚ through SEM analysis. The experimental results of capture efficiency of Cl was when the amount of mixing of two types of LDHs, residual chlorine ions reduced. After 15 mins of ions exchange, the reduction of the amount of ion capture was better when Ca/Al-NO3 LDHs was used. This is because Ca/Al-NO3 LDHs has high the ability of ions exchange affinity. it is identified that interplanar spacing reduced due to the fact that interlayer was exchanged by Cl ion. This is because the radius of NO3 ion in interlayer was only 0.200 ㎚, but the radius of Cl ion was 0.168 ㎚ after ion exchange. It is concluded that LDHs can be producted massively by using co-precipitation, they are able to capture Cl ion. Through later experiment applying to cementitious materials , it should be identified and accessed.