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The method of calibration charts for Monitoring corrosion rates
Author(s) -
Rocchini G.
Publication year - 1997
Publication title -
materials and corrosion
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.487
H-Index - 55
eISSN - 1521-4176
pISSN - 0947-5117
DOI - 10.1002/maco.19970481003
Subject(s) - correctness , corrosion , polarization (electrochemistry) , chart , calibration , function (biology) , mathematics , mathematical analysis , analytical chemistry (journal) , algorithm , materials science , chemistry , statistics , metallurgy , chromatography , evolutionary biology , biology
The definition and meaning of the polarization resistance, after Bonhöffer and Jena , are discussed, and its relationship with the corrosion rate is given. The basic mathematical ideas suitable to introduce the method of calibration charts, first proposed by Skold and Larson , are expounded by considering the current‐voltage characteristic i (Δ E ) = I c (e β E – e‐ β E ) and the correctness of their practical application based on a suitable relationship between I d and R P is proved. Some numerical methods which are useful to compute R P by processing experimental data in the vicinity of β E = 0 or inside intervals as wide as β−50, 50 mV are concisely given. Experimental applications refer to laboratory tests and show that usually I d as a function of R P must be best‐fitted with the function I d ( R p ) = NR P − M , M being different from 1. In the case of iron in 0.5 m H 2 SO 4 solutions, containing some primary aliphatic amines, the corrosion rate takes the form I d = NR P −1 and confirms the goodness of the polarization resistance method, even if the value of the proportionality constant N differs from that one predicted by the theory of Stern and Geary . The results were very satisfactory and proved that the calibration chart method is a valid tool to monitor the reaction kinetics when corrosion is of the uniform type.