The Interface Characterization of 2-Mercapto-1-methylimidazole Corrosion Inhibitor on Brass

Matjaž Finšgar

doi:10.3390/coatings11030295

Abstract

This work presents a detailed surface analytical study and surface characterization, with an emphasis on the X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS) analyses of 2‑mercapto‑1‑methylimidazole (MMI) as a corrosion inhibitor for brass. First, the electrochemical measurements demonstrated a corrosion inhibition effect of MMI in a 3 wt.% NaCl solution. Next, the formation of the MMI surface layer and its properties after 1 month of immersion was analyzed with attenuated total reflectance–Fourier-transform infrared spectroscopy, atomic force microscopy, field-emission scanning electron microscopy, and contact angle analysis. Moreover, to gradually remove the organic surface layer, a gas cluster ion beam (GCIB) sputtering source at different accelerated voltages and cluster sizes was employed. After each sputtering cycle, a high-resolution XPS analysis was performed. Moreover, an angle‑resolved XPS analysis was carried out for the MMI-treated brass sample to analyze the heterogeneous layered structure (the interface of the MMI organic/inorganic brass substrate). The interface properties were also investigated in detail using ToF-SIMS for spectra measurements and 2D imaging. Special attention was devoted to the possible spectral interferences for MMI‑related species. The thermal stability of different MMI-related species using molecular-specific signals without possible spectral interferences was determined by performing a cooling/heating experiment associated with ToF-SIMS measurements. It was shown that these species desorbed from the brass surface in the temperature range of 310–370 °C.

Highlights

Problems related to corrosion represent a huge expense for most countries worldwide [1]
An immersion time of 1 h was sufficient for the MMI surface layer formation, which was not too thick, i.e., the analyses using X-ray photoelectron spectroscopy (XPS) and ToF-SIMS enabled the investigation of the interface properties as well as the simultaneous detection of the organic MMI surface layer and the oxidized brass surface underneath the organic layer
If the brass sample was immersed for more extended periods, the MMI surface layer would become too thick, making the XPS and ToF-SIMS analyses less meaningful for investigating the interface properties, as the signal from the substrate would not be excited

Summary

Introduction

Problems related to corrosion represent a huge expense for most countries worldwide [1]. Organic corrosion inhibitors usually contain S, N, and/or O atoms in their chemical structure They adsorb on the surface from the corrosive solution in a certain manner, forming a surface layer that begins to mitigate corrosion. The manner in which corrosion inhibitors adsorb on the surface and form a surface layer can be determined using advanced analytical techniques such as time-of-flight secondary ion mass spectrometry (ToF-SIMS) and X-ray photoelectron spectroscopy (XPS). These techniques became even more useful for the analysis of organic materials on top of the inorganic materials (metallic materials) with the development of the gas cluster ion beam (GCIB) sputtering source. XPS, angle-resolved XPS (ARXPS), GCIB-XPS, ToF-SIMS spectra, ToF-SIMS imaging, and ToF-SIMS cooling/heating experiments were performed

Sample and Solution Preparation

Electrochemical Measurements

XPS Measurements

ToF-SIMS Measurements