Metal Corrosion Evaluation via Surface Potential Microscopy
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Solution Overview
Problem
Conventional prediction techniques for metal corrosion are not suitable for locally measuring microstructures, making it difficult to detect corrosion pits and estimate the lifetime of metals, especially in duplex phase stainless steel where multiple phases exist with varying chemical compositions.
Innovation Solution
A method using open-loop electric potential microscopy (OL-EPM) to measure surface potential differences in the microstructure of metals immersed in a usage environment liquid, allowing for the prediction of crevice corrosion and pitting depth by calculating the maximum surface potential difference as an evaluation index.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional macro electrochemical measurement is used, then measurement is simple, but local corrosion such as corrosion pits and pitting cannot be detected
Solution Approach 1:
The patent segments the metal surface into multiple measurement regions by moving the probe across different locations. The measurement target is divided into a measurement region and non-measurement regions, allowing localized potential measurements at specific points including grain boundaries and phase interfaces, thereby enabling detection of local corrosion that macro measurements cannot detect.
Solution Approach 2:
The patent replaces conventional macro electrochemical measurement systems with a micro-scale probe-based measurement system. The probe measures local electrochemical potential at microscopic locations on the metal surface, substituting the mechanical macro-measurement approach with a localized micro-measurement approach that can detect corrosion pits and pitting.
2Measurement precision
If immersion test for one year or more is conducted, then corrosion depth can be measured accurately, but evaluation time is too long
Solution Approach 1:
The patent performs preliminary measurement of local electrochemical potential distribution on the metal surface before actual corrosion occurs. By measuring the potential difference at grain boundaries and phase interfaces, the system predicts future corrosion-prone regions and their severity, enabling early evaluation of corrosion resistance without waiting for actual corrosion to develop over long periods.
Solution Approach 2:
The patent establishes a feedback relationship between measured local potential distribution and predicted corrosion behavior. The local electrochemical potential differences measured at various surface locations provide feedback information that correlates with future corrosion depth and location, allowing the system to predict corrosion outcomes based on initial potential measurements rather than waiting for actual corrosion to manifest.
3Measurement precision
If macro chemical composition analysis is used, then analysis is straightforward, but micro phase composition variations cannot be detected
Solution Approach 1:
The patent applies local quality analysis by measuring electrochemical potential at specific local regions including individual grains, grain boundaries, and phase interfaces. Each region's local potential characteristics reflect its specific micro-phase composition and structure, allowing differentiation of micro-phase variations that macro chemical analysis cannot detect. The measurement focuses on locally distinct regions with different corrosion behaviors.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables accurate estimation of crevice corrosion and pitting depth in a short period, reducing the time required for material development and predicting the lifespan of metal structures by identifying local potential distributions and corrosion rates.
Implementation Method 1
measuring a surface potential of a metal under evaluation in a state in which the metal is immersed in a usage-environment liquid
Data Source
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AI summary
The objective of the present invention is to provide a corrosion resistance evaluation method and evaluation device that make it possible to estimate crevice corrosion depth and pitting depth in a short period of time. A corrosion resistance evaluation method according to the present invention is characterized in that the surface potential of a metal under evaluation is measured in a state in which the metal is immersed in a usage-environment liquid, the surface potential distribution of the metal is determined, the surface potential differences in the microstructure of the metal are calculated on the basis of the surface potential distribution, and the corrosion rate of crevice corrosion and corrosion rate of pitting are predicted using the maximum surface potential difference from among the calculated surface potential differences as an evaluation index for corrosion evaluation.