Electric current effect on 8Y-zirconia ceramics : pore migration, grain growth and densification8Y-Zirconia에서 기공이동과 입자성장, 치밀화에 미치는 외부 전류 효과

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The electric current effect was studied in 8 mol% $Y_2O_3$ stabilized $ZrO_2$ ceramics (8YSZ), the leading electrolyte material for Solid Oxide Fuel Cells (SOFCs) and Solid Oxide Electrolysis Cells (SOECs). Since the electrolyte in SOFC/SOEC is under the electrical load at high temperature for a long operation time, we examined their material stability. The present study focuses on the electrically induced microstructure evolution (pore/bubble migration, densification, and grain growth) and those mechanisms. In Chapter 4, electrically induced movement of neutral second phase (pores/bubbles) was investigated in the cubic stabilized zirconia (8YSZ) ceramics using implanted argon bubbles in dense ceramics, and residual sintering pores in porous (75%, 95%) ceramics. Pores/bubbles migrates against the electric field at low temperature $(as low as 875^\circ C)$, where the cation diffusion is supposed to have frozen. The upstream migration of bubbles/pores was evident by the redistribution of porosity and the distorted grain boundaries. The contorted grains, however, were not observed at lower temperature and higher fields when they apparently passed through grain boundaries without causing any visible distortion. The migration mechanism can be attributed to the relocation of atoms around the pore surface by imbalanced ion diffusivity, which yields ${D_{Zr}}^S = 2.8×10^{-6} exp(-174 [kJ/mol]/RT) m^2/s$ : in essence, it is like an electrical Kirkendall effect. In Chapter 5, electrically enhanced densification, called electro-sintering, without the assistance of Joule heating was investigated in 70% dense 8YSZ ceramics at temperatures well below those for conventional sintering. The favored densification to the cathode side can be attributed to electric effect, not to Joule heating, which would leave the center section the hottest, thereby causing it to experience the most densification. Remarkably, full density can be obtained without grain growth under a wide range...
Advisors
Kang, Suk-Joong L.researcher강석중
Description
한국과학기술원 : 신소재공학과,
Publisher
한국과학기술원
Issue Date
2011
Identifier
586363/325007  / 020085030
Language
eng
Description

학위논문(박사) - 한국과학기술원 : 신소재공학과, 2011.8, [ iv, 94 p. ]

Keywords

Microstructure; 치밀화; 입자 성장; 기공 이동; 전기장; 미세구조; Electric Field; Pore Migration; Grain Growth; Densification

URI
http://hdl.handle.net/10203/197336
Link
http://library.kaist.ac.kr/search/detail/view.do?bibCtrlNo=586363&flag=dissertation
Appears in Collection
MS-Theses_Ph.D.(박사논문)
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