[This story appeared on Materials Today (here) a couple of weeks ago]
Australian scientists have demonstrated that graphene flakes grown directly onto stainless steel makes it resistant to corrosion, drawing the attention of the coatings industry.
Hardly a day goes by without mention of another potential application for graphene. Its unique combination of properties has seen it suggested for use in batteries, electronics, filtration systems, composites and coatings. In this latest paper, a team at Deakin University grew 3D networks of graphene nanoflakes on micron-sized fibres of stainless steel, improving both the metal’s resistance to corrosion and its electrical conductivity.
Corrosion is a complex process that is linked to both environmental factors and the conditions of the metal surface (e.g. roughness, surface area and presence of oxides). And although stainless steel is more resistant to corrosion than other metals, in acidic, aqueous environments, it can be susceptible to localised forms of attack that can result in cracking. Published in the April issue of Carbon [DOI: 10.1016/j.carbon.2015.02.042], Deakin’s work utilises the natural hydrophobic properties of graphene to repel water from the surface of stainless steel fibres. In addition, graphene’s electrical properties reduce the likelihood of redox reactions occurring on the surface, preventing oxidation of the substrate metal.
Led by Lingxue Kong, the team coated highly-porous austenitic substrates – consisting of evenly-distributed 15µm diameter steel fibres – with networks of carbon nanoflakes. By tuning the temperature and feed gas flow rate during growth, the thickness of graphene coating could be tightly controlled. The resulting coating varied from a few atomic layers thick, to complex, interconnected nanopillars of carbon which increased the specific surface area of the material by up to 26,000 times.
The inhomogeneity of stainless steel’s microstructure was found to produce a graphene coating that was not highly-crystalline. In addition, the wettability of the material was also studied, and it was found that when the density of carbon nanopillars was highest, the coated steel was super-hydrophobic. The material also displayed its highest corrosion resistance to synthetic seawater at this point, suggesting that it was the presence of graphene that increased its corrosion resistance, without compromising the properties or structure of the native stainless steel material.
The team expect potential applications of their coated-steel to include thermal exchangers, molecular separation systems and bio-compatible materials.
Carbon 87 (2015) 395–408, “Growth of nano-textured graphene coatings across highly porous stainless steel supports towards corrosion resistant coatings” DOI: 10.1016/j.carbon.2015.02.042