Metal Foam in Scanning Electron Microscope, magnification 10x. Image: Wikimedia Commons

New method boosts resistance of stainless steel

15 November 2023

A team of HKU researchers have developed a dual-action approach which improves the performance of stainless steel and could be used in the production of hydrogen.

Stainless steel, first discovered by English metallurgist Harry Brearley in 1913, is valued for its anti-corrosion properties. Over 50 million tonnes of stainless steel are produced globally each year.

Cromium-based passive films play an essential role in establishing the anti-corrosion characteristics of conventional stainless steel. However if conditions become too extreme, for example if the steel is used in a very acidic environment or exposed to very high electrical potentials, the protective layer can break down. Pitting or transmissive corrosion can lead to corrosion-induced failure of equipment and infrastructure with corresponding economic losses and safety implications.

To improve corrosion-resistance, other elements including molybdenum, nitrogen or copper are added to chromium. The resulting alloys exhibit good resistance in saline environments. However the passive layer can still break down when it is exposed to very high electrical charges. This limits the use of stainless steel in applications which require a saline solution and a high potential charge, for example the production of hydrogen from sea-water.

To address these limitation, Professor Mingxin Huang of the Department of Mechanical Engineering of the University and his colleagues developed a novel alloy containing the element manganese. A secondary manganese-based layer forms on top of the chromium-based layer giving the new alloy remarkable anti-corrosion properties including when exposed to high electrical charges.

It took the team over six years from the time of their initial discovery to develop their sequential dual-passivation strategy which has many possible applications in industry. Their findings are published in Materials Today.

Their alloy has the potential to dramatically reduce the cost of materials used in the production of hydrogen from sea water. To prevent corrosion, expensive silver- and platinum-coated titanium alloys are commonly used in hydrogen production today. The HKU team estimates that using stainless steel could reduce the cost of such equipment by more than 40 times.

“From experimental materials to real products such as meshes and foams for water electrolysis we are moving forward in applying our more economical stainless steel in hydrogen production from renewable sources,” said Professor Huang.

Professor Minxing Huang was awarded a Croucher Senior Research Fellowship in 2022. To view his Croucher profile click here.