IIT Bombay researchers find a technique to measure degradation of iron coatings

A team of researchers at the Indian Institute of Technology (IIT) – Bombay have come up with a new technique that can measure the rate of iron coating degradation. This discovery claims to hold the potential of benefiting the steel industry. Metals corrode with time, and some metals corrode more than others, like iron rusts in days, while gold and silver take decades or centuries to deteriorate. According to a recent market analysis report by Grand View Research, the market for such corrosion inhibitors is a $8.93 billion market projected to grow at 3.6% annually from 2025 to 2030.

Metals often have a layer of protective coating, like the paint on cars, to prevent corrosion. A more efficient way of protecting metals is by coating them with organic coatings that are basically layers of carbon-based polymeric substances, natural or synthetic, applied in the form of paints and varnishes. However, the efficiency of organic coatings deteriorates with time because the coatings have pores and defects that allow water and oxygen to reach the underlying metal surface over time and corrode it.

The coating wears with time because of a fundamental electrochemical process called oxygen reduction reaction (ORR), where molecular oxygen gets reduced to water or hydrogen peroxide or hydroxyl ions. This process occurs in various electrochemical devices, including fuel cells and metal-air batteries.

A couple of years ago, a team of researchers led by Professor Vijayshankar Dandapani at the Department of Metallurgical Engineering and Materials Science at IIT Bombay established an improved quantitative method to characterise the performance of organic coatings used for corrosion protection. The researchers combined hydrogen permeation-based potentiometry (HPP) with electrochemical impedance spectroscopy (EIS) and this technique allowed the researchers to quantify the degradation rates at the interface between the organic coating and the metal. While HPP gives a direct measure of hydrogen permeation, EIS provides insights into how hydrogen permeation corrodes the coated metal. 

Mr. Dandapani said, “The idea itself came from an attempt to find if a complementary technique such as EIS can be used to strengthen the interpretations from the HPP approach.”

In an earlier study, Mr. Dandapani said that the researchers provided proof-of-concept by measuring ORR at the interface between a model polymer coating and palladium metal using HPP and EIS. In this new study, the IIT Bombay’s team along with researchers from the University in Brest, France, have extended this application to an important industrial metal, iron.

This study received funding from the Indo-French Centre for Promotion of Advanced Research -CEFIPRA and the Science and Engineering Research Board (SERB), India.

“We coated a thin layer of iron on palladium membranes and coated the iron with a polymer called poly-methyl methacrylate (PMMA). They measured the rate at which oxygen reduction reaction occurred at the interface between PMMA and iron using HPP-EIS. They captured the current-potential (I(U)) curves and corresponding impedance values, which they found to be higher than that for a bare iron surface. High impedance values correspond to low corrosion rates and vice versa. The combined usage of HPP-EIS also gave a clearer picture of ORR happening at the interface between the iron surface and the organic coating, more than either of them could individually and validated the use of the HPP-EIS technique to evaluate ORR occurring at interfaces that one cannot easily study using the traditional methods because the interface between organic coatings and metals is buried and inaccessible,” Mr. Dandapani explained.

HPP-EIS is cost-effective because it requires only two potentiostats, simple electronic devices that control and measure the voltage between two electrodes. Mr. Dandapani said that HPP-EIS can be used to monitor how quickly the organic coating will give way for the iron to rust, and that the method would be of interest not only to the steel industry but will also be useful in the field of fuel cells and sensors.

With hydrogen blending becoming increasingly popular to reduce emissions from natural gas, one can also apply the HPP-EIS technique to determine how quickly the coat of paint on a natural gas pipeline, where hydrogen is blended with natural gas, degrades, Mr. Dandapani said highlighting a potential application.