소듐붕규산염 유리의 표면 구조에 대한 분자 동역학 시뮬레이션 연구 = Na Borosilicate Glass Surface Structures: A Classical Molecular Dynamics Simulations Study

국문 초록 (Abstract)

핵폐기물을 고화시키는 재료로 사용하는 붕규산염, borosilicate, 유리의 용해는 지충 처분장에 처리된 고준위 방사성 폐기물의 생태적 유출을 결정할 수 있는 중요한 화학반응이다. 습식 실험에서 유리의 용해속도, dissolution rate, 는 유리 화학조성에 의해 크게 좌우되는 것이 관찰된다. 유리의 bulk 구조의 규명한 분광분석 실험에 의하면 유리의 화학조성과 분자수준, molecular-level, 구조, 예: SiO4사면체의 연결구조와 B 원소의 배위구조, 사이의 상관관계가 존재한다. 따라서 화학조성에 따른 유리 용해도의 차이는 조성에 따른 bulk 내부구조의 변화로 이해되어 왔다. 그런데 유리표면은 수용액과 계면을 이루면서 용해과정에서 가장 직접적으로 반응하는 부분이기 때문에, 화학조성에 따른 표면구조 변화에 대한 지식 또한 필요하다. 본 논문에서는 분자 동역학, mo;ocu;ar dynamics, MD, 시뮬레이션을 사용하여 4가지의 다른 화학조성을 가지는 소듐붕규산염 유리, xNA2O.B2O3.ySiO2 화학조성, 에 대하여 bulk구조와 실험으로 얻기 어려운 표면, surface, 구조를 연구하였다. MD 시뮬레이션은 유리표면의 화학조성과 분자수준 구조가 bulk의 것과 매우 상이한 결과를 보여준다. 본 연구의 MD 시뮬레이션 결과는 화학조성에 따른 유리 용해도, 특히 초기 용해과정, 는 bulk구조의 변화보다 유리 표면구조의 변화에 의해 크게 좌우될 수 있다는 표면구조에 대한 이해의 중요성을 역설한다.

다국어 초록 (Multilingual Abstract)

Borosilicate glass dissolution is an important chemical process that impacts the glass durability as nuclear waste form that may be used for high-level radioactive waste disposal. Experi-ments reported that the glass dissolution rates are strongly dependent on the bulk composition. Because some relationship exists between glass composition and molecular-structure distribution, eg, non-brid-ging oxygen content of SiO4 unit and averaged coordination number of B), the composition-dependent dissolution rates are attributed to the bulk structural changes corresponding to the compesitional variation, We examined Na borosilicate glass structures by performing classical molecular dynamics, MD, simulations for four different chemical compositions, xNa2O.B2O3.ySiO2, Our MD simulations de-monstrate that glass surfaces have significantly different chemical compositions and structures from the bulk glasses. Because glass surfaces forming an interface with solution are most likely the first dissolution-reaction occurring areas, the current MD result simply that composition-dependent glass dissolution behaviors should be understood by surface structural change upon the chemical composition change.

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