Simulation of Outdoor Atmospheric Corrosion of Carbon Steel in Wet Tropics from Three-Month and One-Year Tests

P. V. Strekalov* and Do Thanh Binh**

* Institute of Physical Chemistry, Russian Academy of Sciences,
Leninskii pr. 31, Moscow, 119991 Russia

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** Institute of Tropical Technology, Vietnamese Academy of Sciences and Technology,
Hoang Quoc Viet, Hanoi, Vietnam

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Received September 16, 2004

Abstract — Mathematical models of the kinetics of outdoor atmospheric corrosion of metals were approved for a plain 3 carbon steel in the wet tropics of Vietnam and periods from 0.5 to 10 years by the results of 3-month and one-year outdoor atmospheric tests. The least deviation of the predicted from actually observed corrosion rate were observed for the time periods ranging from 1.5 to 2 years (the minimum error = 0.05%; the maximum = 12.7%). The average error of the predicted estimates, for all the models employed, falls into a rangefrom 10.9 to 41.4% for 3–5 years. However, for 10 years, it ranges either from 39.9 to 62.5% or from 4.8 to 38.9% depending on whether the results of 3-month or one-year outdoor tests were used, respectively. Past century data on the corrosion resistance of a 3 steel were also used as the initial, whereas the calculated corrosion rates were compared to the most recent results of testing the steel in the rural atmosphere of North Vietnam (suburban district of Hanoi). The maximum prediction error ( = 23–139%) corresponds to calculations based on the tests for three winter months; the minimum (= 8–54%), to those for three months in summer.

Kinetic Parameters and Mechanism of Gold Electrooxidation in Thiocarbamide Solutions

L. F. Kozin*, S. A. Kozina**, and A. K. Bogdanova*

* Vernadsky Institute of General and Inorganic Chemistry, National Academy of Sciences of Ukraine,
pr. Akademika Palladina 32/34, Kiev-142, 03680 Ukraine

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** Dumanskii Institute of Colloid and Water Chemistry, National Academy of Sciences of Ukraine,
bulv. Vernadskogo 42, Kiev-142, 03680 Ukraine

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Received January 23, 2003

Abstract — Kinetics and mechanism of gold electrooxidation in sulfuric acid solutions of thiocarbamide (TCA) are studied by measuring voltammograms (VA) of gold and glassy carbon (GC) electrodes. In a potential (E) range from –0.2 to 1.2 V (SCE), VA of a gold electrode demonstrate three peaks. The first and the second peaks correspond to gold electrooxidation to [AuTCA_ads]⁺ and [Au(TCA_ads)₃]³⁺ ions at E of 0.152 and 0.554 V, while the third one corresponds to TCA electrooxidation. The electrooxidation of TCA on GC electrodes is characterized by two VA peaks at 0.983 and 1.437 V. The first peak corresponds to the formation of formamidine dis-ulfide (FADS) (k_a1 = 6.4010⁴ cm/s), while the second peak corresponds to TCA oxidation to sulfides and hydrosulfides (k_a2 = 7.7810⁵ cm/s). The composition of adsorption layers formed at the Au electrode is ana-lyzed by Auger spectroscopy. The introduction of sodium sulfide into TCA solutions eliminates the formation of adsorption layers and accelerates Au oxidation in such solutions. The rate constants of gold electrooxidation k_a = 6.31 10^–3 cm/s and Au(I) electroreduction k_c = 5.46 10^–4 cm/s in TCA solutions are estimated. Kinetic parameters (charge transfer coefficients, reactions orders in carbamide) are determined and the mechanisms of Au and TCA oxidation in sulfuric acid solutions are proposed.

Kinetics of Galvanostatic Chloride Pitting of Stainless Steels in Chloride Solutions

I. I. Zamaletdinov

Perm State Technical University, Komsomol’skii pr. 29a, Perm, 614600 Russia

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Received March 12, 2001; in final form, July 15, 2003

Abstract — To check the theory, the corrosion of steels 121810 and 1017132 is studied during galvanostatic polarization at different , current densities, and temperatures. The morphology and size distribution of pits are discussed. In E vs. log curves are shown to demonstrate a single linear segment for steel 121810 and two linear segments for 1017132 (as for pure Fe, according to the literature data [12]), namely, the initial segment with a steep slope and the later one with more gentle slope. The single slope E/of steel 121810 and the later (gentle) slope, which is observed for both steel 1017132 and Fe, correspond to those predicted in [3, 4, 7], while the earlier steep slope corresponds to crevice-type pitting.