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PEO 코팅 처리된 AZ91 합금의 산화층에 미치는 후-열처리의 영향
김용민(Y. M. Kim),고영건(Y. G. Ko),신동혁(D. H. Shin) 한국소성가공학회 2009 한국소성가공학회 학술대회 논문집 Vol.2009 No.10
The influence of the subsequent-annealing (SA) treatment on plasma electrolytic oxidation (PEO)-treated Mg-based alloy was investigated and the dependence of the dehydration reaction on the SA temperature was also studied. For this purpose, a series of the SA treatments were carried out on the coated samples at two different temperatures, i. e. 423 and 523 K for 10 h. In contrast to the sample without SA treatment, the sample annealed at 523 K exhibited a significant difference in term of surface morphology since the MgO content in the oxide layer increased with increasing SA temperature. With increasing SA temperature, the dehydration of Mg(OH)₂ led to the increase in the relative amount of the MgO, which was a hard phase. From the nano-indentation results, the applied loads of the samples were seen to increase as SA temperature increased. However, the corrosion resistance of the sample annealed at 423 K was higher than that of the samples annealed at 523 K.
Microprobe EELS Study of Oxygen Non - Stoichiometry in High Tc YBa₂Cu₂₃O7-δ Grain Boundaries
신동혁(D. H. Shin),S. E. Babcock(S. E. Babcock) 한국진공학회(ASCT) 1995 Applied Science and Convergence Technology Vol.4 No.2
2~3 ㎚의 공간분해능을 갖는 전자에너지손실분광법(Electron Energy Loss Spectroscopy, EELS)을 이용하여, 전기적 특성조사된 YBa₂Cu₂₃O_(7-δ) 고온초전도체 쌍결정의 결정경계(grain boundary)에서 산소의 조성변화를 조사하였다. Misorientation angle이 14˚, 28˚, 30˚인 3개의 쌍결정 중에서 Josephson junction 특성을 보인 28˚ 및 30˚ 결정경계에서의 oxygen 1s absorption edge는 결정내부에서의 oxygen 1s absorption edge와 매우 다름을 알 수 있었다. 이는 결정경계에서의 산소조성이 결정내부에 비해 낮음을 의미하며, 그 영역이 결정경계 부근 20~40 ㎚로, coherence length에 비해 큼을 알 수 있다. 반면에, flux pinning 특성을 보인 14˚ 결정경계에서의 oxygen 1s absorption edge는 결정내부에서와 별 차이를 보이지 않았다. 따라서 일반적으로 관찰되어온, misorientation angle이 큰 결정경계에서의 Josephson junction 특성은 결정경계 부근에서 산소의 조성이 낮아지는데에 기인하며, 그 원인은 결정경계면을 통해 산소가 out-diffusion 되기 때문인 것으로 생각된다. The oxygen concentration at grain boundaries in electromagnetically-characterized, bulk-scale bicrystals of high T_c, YBa₂Cu₂₃O_(7-δ) has been investigated using high-spatial resolution (2~3 ㎚) electron energy loss spectroscopy (EELS) in a TEM. Flux-grown bicrystals containing grain boundaries with misorientation relationships of 14°, 28°, and 30° about [001] have been studied. The 14° bicrystal showed flux-pinning (FP) critical current density characteristics, whereas the 28° and 30° bicrystals behaved like Josephson Junctions (JJ). The oxygen 1s absorption edge observed at the grain boundaries of Josephson junction bicrystals by TEM-EELS has a markedly different structure than those of the intragranular regions. The difference indicates a depressed charge carrier density and oxygen concentration in the boundary region. The carrier deficient zone extends from 20 to 40 ㎚ into each crystal, a distance much larger than a coherence length in the direction perpendicular to the boundary. In striking contrast, the oxygen K-edges in spectra taken from the grain boundary with flux-pinning character are nearly identical to the intra granular spectra. The observed oxygen deficiency of the Josephson junction boundaries is consistent with a model in which the high-angle boundaries provide high-diffusivity paths for the oxygen diffusion out of the sample.