Abstract
Employing atomic force microscopy (AFM) to measure passive film thickness on stainless steel (SS) in aqueous solution is proposed. SUS304 austenite and SUS329J4L duplex SS samples partly covered by gold were set in a minicell. To remove the original film, the SS surface but gold was etched using dilute sulfuric acid. After cleaning, open circuit potential (OCP), and distance from the sample surface to the top of the gold were measured. They were then immersed in either 1.0% NaCl; 5.0% NaCl; or aqueous solution with pH ranging from 1.0 to 10.0 and measured again. Differences between the first and subsequent measures of OCP suggested a passive film had formed in solution with pH ranging from 2.8 to 10.0. Similarly, differences among AFM measures revealed the observed film thickness increased with increase in pH and with decrease in chloride ions. Also, film thickness in water was greater than that in a vacuum. Comparison of AFM measurements of passive film on the austenite and sigma phases in sensitized SUS329J4L duplex SS revealed the film was thinner on the sigma phase containing more chromium. Taken together, these findings suggest the proposed method is applicable for measuring the thickness of passive films in aqueous solution.
Highlights
Passive film on stainless steel (SS) has been analyzed using various technologies and methods, including TEM1, XPS2, AES3, SIMS4, GDS5, XAFS6, MU-VRS7, Raman spectroscopy[8,9,10,11], ellipsometry[11,12,13,14,15] and potential-modulated reflection spectroscopy (PMRS)[11,15,16,17,18]
According to the few reports on in situ analysis of the composition of passive film, PMRS reveals the ratio of metal elements in only the top 0.5 nm[16,17,18] of the film, and Raman spectroscopy is not sufficiently sensitive to determine the composition of a very thin passive film[11]
The open circuit potential (OCP) sharply decreased to below −350 mV vs. SSE when the sample was immersed in sulfuric acid, indicating the passive film had completely dissolved, exposing bare substrate
Summary
Passive film on SS has been analyzed using various technologies and methods, including TEM1, XPS2, AES3, SIMS4, GDS5, XAFS6, MU-VRS7, Raman spectroscopy[8,9,10,11], ellipsometry[11,12,13,14,15] and potential-modulated reflection spectroscopy (PMRS)[11,15,16,17,18]. Scanning probe microscopy (SPM) including scanning tunneling microscopy (STM) and atomic force microscopy (AFM) have emerged as potential methods to investigate passive films of nanometer order at the metal/ environment interface. The lateral resolution of AFM is low when observing steep steps, and usually the obtained morphology is affected by the shape of the probe tip This makes it difficult to obtain cross-sectional views of passive film using AFM in situ by current methods. The measurements were obtained using a custom designed minicell and AFM with a vertical resolution of ~0.01 nm to precisely measure passive film thickness. This method should be useful for researching corrosion mechanisms and the growth of passive films on SS in situ
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
