Corrosion is an age-old problem, but some of the latest solutions are distinctly 21st century.
Corrosion has been a problem for as long as human have used metals – it’s no coincidence that the metals we consider most precious are those that do not corrode. Protecting metals that do corrode has involved various surface treatments, from simply painting the surface to current magnesium iron phosphate ceramic coatings for steel. Chemicals that could slow down corrosion, known as corrosion inhibitors, have been widely used in paints since the industrial revolution. But over the past decade, new types of nanostructured protective coatings have been developed that provide better corrosion protection – some delivering corrosion inhibitor only when needed, others able to heal themselves and remove flaws vulnerable to corrosion. Using clever chemistry, corrosion scientists are finding greener and longer-lasting solutions.
Today, corrosion still has a massive economic impact. The global cost of corrosion is estimated to be US$2.5 trillion (£1.9 trillion), which is equivalent to 3.4% of global GDP. Corrosion impacts on infrastructure, transport and major sectors like the oil and gas industry, who will spend millions on corrosion monitoring and maintenance activities. So why is corrosion still a problem? With all our ingenuity, why haven’t we found a solution? The answer is thermodynamics. ‘There is no foolproof solution to the problem,’ explains Mikhail Zheludkevich from the Helmholtz Centre for Materials and Coastal Research in Geesthacht, Germany. ‘All the structural metals are thermodynamically unstable and are oxidised, which causes corrosion. The only possibility is to delay the process.’
Slowing down corrosion can be achieved to some extent, and most metals used in construction will have coatings containing corrosion-inhibiting chemicals. Some of the most successful once contained chromium(vi) compounds, which form a passivating chromium oxyhydroxide layer. ‘We thought we had this figured out, but then it turned out that chromium is highly carcinogenic, so in the last 20 years or so we have had to go back to the drawing board,’ explains chemist Sarbajit Banerjee from Texas A&M University in the US. Chromium(vi) compounds are now banned in Europe and the US.
Read more: The nanocoatings holding back corrosion