On the passive films and anodic behavior of samarium in various aqueous solutions

Journal Article · Mon Jun 01 00:00:00 EDT 1992 · Journal of the Electrochemical Society; (United States)

DOI:https://doi.org/10.1149/1.2069460· OSTI ID:7237509

Yang, H H ^[1]; Hara, N; Sugimoto, K ^[2]

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1. Dept. of Metallurgical Engineering, Inha Technical Junior College, Inchon 160 (KR)
2. Tohoku Univ., Sendai (Japan). Faculty of Engineering

This paper reports on anodic polarization curves of Sm that have been measured in solutions of phosphate (pH 1.53-6.86), borate (pH 8.45 and 10.4), 01 kmol {center dot} m{sup {minus}3} NaOH (pH 13.1), 0.005 kmol {center dot} m{sup {minus}3} Na{sub 2}SO{sub 4} (pH 5.3), and 0.005 kmol {center dot} m{sup {minus}3} NaCl (ph 5.3). Surface films formed on Sm in these solutions have been examined by using in situ ellipsometry, x-ray photoelectron spectroscopy (XPS), and infrared absorption spectroscopy (IRS). It was found that in the phosphate, borate, and NaOH solutions Sm passivates spontaneously at corrosion potentials even at acidic pH and shows wide passive ranges until the transpassive dissolution occurs at higher potentials. In the Na{sub 2}SO{sub 4} and NaCl solutions, however, Sm dissolves actively at potentials higher than corrosion potentials and does not passivate. The thickness and optical constants of passive films on Sm, which were determined by ellipsometry, depends on the composition and pH of the solutions and the electrode potential; the thickness of passive films increased from 4.6 to 15.9 nm in phosphate (pH 6.86), from 9.0 to 170 nm in borate (pH 8.45), and from 2.1 to 9.0 nm in NaOH (pH 13.1), respectively, with increasing potential. In an acidic phosphate solution (pH 2.98), thicker films ({gt}150 nm) were formed at low potentials in the passive region. The transpassive dissolution caused a sharp increase in the film thickness and a decrease in the real part of the complex refractive index. From XPS and IRS analyses, it is suggested that the passive and transpassive films formed in phosphate solutions contain Sm(III) phosphate, and those in borate and NaOH solutions consist of Sm(III) oxide and hydroxide.

• OSTI ID: 7237509
• Journal Information: Journal of the Electrochemical Society; (United States), Vol. 139:6; ISSN 0013-4651
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
36 MATERIALS SCIENCE
SAMARIUM
ANODES
POLARIZATION
THIN FILMS
X-RAY SPECTRA
ABSORPTION SPECTRA
AQUEOUS SOLUTIONS
BORATES
ELLIPSOMETRY
PH VALUE
PHOSPHATES
REDOX POTENTIAL
SODIUM HYDROXIDES
ALKALI METAL COMPOUNDS
BORON COMPOUNDS
DISPERSIONS
ELECTRODES
ELEMENTS
FILMS
HYDROGEN COMPOUNDS
HYDROXIDES
MEASURING METHODS
METALS
MIXTURES
OXYGEN COMPOUNDS
PHOSPHORUS COMPOUNDS
RARE EARTHS
SODIUM COMPOUNDS
SOLUTIONS
SPECTRA
400400* - Electrochemistry
360606 - Other Materials- Physical Properties- (1992-)