• Nuclear Engineering and Technology
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• 제50권3호
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• pp.416-424
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• 2018

Microstructure of oxide formed on Zr-Nb-Sn tube sample was intensively examined by scanning transmission electron microscopy after exposure to simulated primary water chemistry conditions of various concentrations of Zn (0 or 30 ppb) and dissolved hydrogen ($H_2$) (30 or 50 cc/kg) for various durations without applying desirable heat flux. Microstructural analysis indicated that there was no noticeable change in the microstructure of the oxide corresponding to water chemistry changes within the test duration of 100 days (pretransition stage) and no significant difference in the overall thickness of the oxide layer. Equiaxed grains with nano-size pores along the grain boundaries and microcracks were dominant near the water/oxide interface, regardless of water chemistry conditions. As the metal/oxide interface was approached, the number of pores tended to decrease. However, there was no significant effect of $H_2$ concentration between 30 cc/kg and 50 cc/kg on the corrosion of the oxide after free immersion in water at $360^{\circ}C$. The adsorption of Zn on the cladding surface was observed by X-ray photoelectron spectroscopy and detected as ZnO on the outer oxide surface. From the perspective of $OH^-$ ion diffusion and porosity formation, the absence of noticeable effects was discussed further.

• 한국세라믹학회지
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• 제43권11호
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• pp.724-727
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• 2006

It has long been known that the oxidation kinetics of Zr-based alloys undergoes a crossover from parabolic to cubic in the pretransition period (before breakaway of the oxide scale). This kinetic crossover, however, is not fully understood yet. We have earlier proposed a model for the Zr-oxidation kinetics, in a closed form for the first time, by taking into account a compressive strain energy gradient as a diffusional driving force in addition to a chemical potential gradient of component oxygen across the ZrO$_2$ scale upon Zr [J. Nucl. Mater., 299 (2001) 235]. In this paper, we experimentally reconfirm the validity of the proposed model by using the thermogravimetric data on mass gain of Zr in a plate and wire form, respectively, in air atmosphere at different temperatures in the range of 500$^{\circ}$ to 800$^{\circ}C$, and subsequently report on the numerical values for oxygen chemical diffusivity and strain energy gradient across the oxide scale.

• 한국재료학회지
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• 제8권4호
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• pp.368-374
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• 1998

Zr합금의 부식거동을 평가하기 위하여 여러 가지 1족 알칼리 수산화물 용액 (LiOH, NaOH, KOH, RbOH, CsOH)에서 autoclave를 이용하여 300일까지 부식시험을 실시하였다. 산화막 특성은 TEM을 이용하여 천이전과 천이후에 동일 산화막두께를 갖도록 준비된 부식시편에 대해 수행되었다. 실험결과를 고려할 때 금속이온은 부식과정에서 매우 중요한 역할을 하는 것으로 사료된다. 즉 $Li^+$가 $Zr^{4+}$ 치환하여 산소농도는 증가하고 부식은 가속되는데 산화막 내부의 barrier layer에서 $Li^-$치환이 부식을 제어하는 것으로 판단된다.동일 두께의 산화막 일지라도 산화막의 구조는 모두 다르다. 32.5mmol LiOH에서 생성된 산화막온 천이전,후에 관계 없이 많은 기공이 함유된 등축정 구조를 갖는다. 반면에 NaOH에서 생성된 산화막은 천이전에는 주상정 구조를 갖지만 천이후에는 다공성의 등축정 구조로 바뀐다. KOH용액에서는 천이전에는 주상정과 비정질 산화막의 이중 구조를 갖지만 천이후에는 비정질 산화막은 사라직 전반적으로 주상정 구조가 형성된다. 부식거동과 산화막 관찰로부터 금속이온의 산화막내 치환이 부식속도와 산화막 미세구조를 지어한다는 것을 알 수 있었다.