The corrosion mechanism initiation of a 75Sn–25Pb coating on a low‐carbon steel sample in HCl environments

Abstract

The corrosion of a 75Sn-25Pb coating on low-carbon steel exposed to a vapor/ condensate phase over a 1 mol/L HCl solution has been studied. The corrosion mechanism initiation was based on several steps. The presence of CO 2 and lead involves the precipitation of cerussite PbCO 3 crystals. Overtime, the cerussite evolved and transformed into PbCl 2 . This transformation was not direct and involved the creation of reaction intermediates whose chemical composition was variable. In parallel, tin formed oxides that were not stable in the HCl solution. These oxides dissolved and led to the formation of an electrolyte concentrated in Sn 2+ . When tin ions' saturation was reached, tin precipitated to form abhurite, Sn 21 Cl 16 (OH) 14 O 6 , or hydrated tin chloride, SnCl 2 .2H 2 O. This study highlighted the particularity of the corrosion mechanism. It also showed that the presence of tin promoted the oxidation of lead and consequently the formation of cerussite.

Modelling of Lead Corrosion in Contact with an Anaerobic HCl Solution, Influence of the Corrosion Product Presence

“…The dissolution of the material leads to the formation of 2+ valence ions, which concentrate the electrolyte, particularly near the surface of the electrode. The value of the concentration of lead ions is higher than the solubility limit creating a saturation of the electrolyte, as is in agreement with the experimental results that show a tendency to passivation, as materialized by the precipitation of PbCl 2 at the Pb surface [40,41].…”

“…Initially islands of PbCl2 are created then grow until they form a compact and fissured layer. In this sense, a porous corrosion product layer was initially placed to simulate these islands [41].…”

“…With this decomposition appears the need to pose several hypotheses and the establishment of artificial criteria determining the passage from one to the other [46]. Experimentally, the growth and agglomeration phases of PbCl 2 have been observed on the surface of lead in contact with a humid environment polluted by HCl [40,41]. Taking into account the creation of this layer is therefore a necessary step for the implementation of the global corrosion process.…”

What happens when a Pb–Sn coating deposited on low carbon steel is exposed in an HCl‐polluted wet environment? Development of a corrosion mechanism

“…[27] In parallel, tin precipitates in the form of hydrated corrosion products composed of tin, oxygen, and chlorine, such as abhurite or hydrated tin chloride, SnCl 2 •2H 2 O. [28] Nevertheless, although a few stages of the mechanism have been identified, no comprehensive mechanism that can explain the failures has been established, due to the fact that these failures are not easily detected during subsequent failure analysis. [12] The purpose of this article is to synthesize all the results obtained to establish a global corrosion mechanism when a Pb-Sn coating deposited on low carbon steel is corroded in an HCl-polluted wet environment.…”

“…[ 27 ] In parallel, tin precipitates in the form of hydrated corrosion products composed of tin, oxygen, and chlorine, such as abhurite or hydrated tin chloride, SnCl 2 · 2H 2 O. [ 28 ] Nevertheless, although a few stages of the mechanism have been identified, no comprehensive mechanism that can explain the failures has been established, due to the fact that these failures are not easily detected during subsequent failure analysis. [ 12 ]…”