서지주요정보
(A) study on the metastable pitting behavior of austenitic stainless steel by the electrochemical noise analysis = 전기 화학 잡음 분석법에 의한 오스테나이트 스테인리스강의 준안정 공식거동에 관한 연구
서명 / 저자 (A) study on the metastable pitting behavior of austenitic stainless steel by the electrochemical noise analysis = 전기 화학 잡음 분석법에 의한 오스테나이트 스테인리스강의 준안정 공식거동에 관한 연구 / Ji-Ho Kang.
발행사항 [대전 : 한국과학기술원, 2000].
Online Access 원문보기 원문인쇄

소장정보

등록번호

8011054

소장위치/청구기호

학술문화관(문화관) 보존서고

MMS 00004

휴대폰 전송

도서상태

이용가능

대출가능

반납예정일

리뷰정보

초록정보

Noise is a general term used to describe the fluctuating behavior of a physical variable with time. In the electrochemical process one may measure either the voltage or current fluctuation with time, so they can be called to electrochemical noises. The analysis of electrochemical noise is now considered to give useful information about the rate and the nature of electrochemical reactions taking place at the electrode. In recent studies the noise from the current transient under the potentiostatic condition is ascribe to events - film breakdown and repair : metastable pitting, although the theoretical basis of the interpretation is somewhat limited. In this study, the current transients generated during metastable pitting of austenitic stainless steels immersed in solutions containing chloride were monitored and analyzed under potentiostatic control by electrochemical noise technique. 1. PSD analysis The current transients generated during metastable pitting of austenitic stainless steels immersed in various conditions were monitored. With increasing chloride concentration, applied potential, and temperature, the magnitude of PSD is increasing due to the events with high current density. It is indicated that the stability of the passive film is decreasing with increasing chloride concentration, applied potential, and temperature. And the cut-off frequency in which the PSD magnitude decreases abruptly shifts to the high frequency region. Even though the PSD slope became steep with increasing corrosivity, that relationship is not clear because of many scattered data. However, in terms of passivation time, the PSD slope approaches to the zero with increasing the passivation time. It means the magnitude of PSD is not changed through the whole frequency due to reducing the number of current spike in stable passive film. 2. Metastable pitting potential By the current transients generated during metastable pitting of austenitic stainless steels in potentiostatic condition the critical metastable potential can be acquired. The critical metastable potential is the potential at which the metastable pits start to propagate for short period. Events become greater with increasing applied potential and reaches a maximum value - transition potential. The presence of the transition potential is due to the elimination of susceptible nucleation sites for metastable pitting in a given potential. Like the pitting potential, the critical metastable pitting potential has the logarithmic relationship with chloride concentration. So, the Modified Point Defect Model can explain the initiation of the metastable pit. The critical amount for initiating metastable pitting, ξ'', is quite small comparing to ξ, the critical amount stable pitting. 3. Criteria for the transition from metastable to stable pitting Using the assumption of hemispherical metastable pit shape, the metastable pit current density can be calculated. The metastable pit size distribution was analyzed in terms of the metastable pit current density as a function of the peak current in current transient. The metastable pits yielded peak currents between ~$10^{-7}$ and ~$10^{-5}$ A, metastable pit current densities at peak current between ~0.01 and ~1 A/㎠, and metastable pit radii at peak current between ~2 and ~15 mm. As the potential is increased, the metastable peak currents and pit radii at peak current both increase toward line. As potential is increased, the metastable peak currents and pit radii at peak current both increase toward $\frac{I_{pit}}{R_{pit}} = 3\times 10^{-3}$ line. This is the boundary for dividing the stable pits and metastable pits.

서지기타정보

서지기타정보
청구기호 {MMS 00004
형태사항 86 p. : 삽화 ; 26 cm
언어 영어
일반주기 저자명의 한글표기 : 강지호
지도교수의 영문표기 : Hyuk-Sang Kwon
지도교수의 한글표기 : 권혁상
학위논문 학위논문(석사) - 한국과학기술원 : 재료공학과,
서지주기 Reference : p. 82-86
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