'Nano-alloy' fabrication method has promise for new materials

It is claimed their discovery may change how the form and structure of nanomaterials are manipulated, particularly those used for gas storage, heterogeneous catalysis and lithium-ion batteries.

The findings are the subject of an article in the journal Small, co-authored by associate professor Mathew M. Maye and research assistant Wenjie Wu.

Until now, scientists have used many wet-chemical approaches to manipulate reactions in which metallic ions form alloys at the nanoscale. Here, metal nanoparticles are typically 2 to 50 nanometres in size and have unique properties, including high reactivity and novel chemistry.

‘At SU, we have developed a new synthetic pathway to tailor the internal microstructure of nanomaterials,’ Maye said in a statement.

Maye’s approach begins with a pre-synthesised iron nanoparticle core. After synthesising the core in its crystalline metallic form, he and Wu chemically deposit thin shells of chromium onto the iron.

When the core/shell nanoparticles are exposed to high temperatures, they anneal. Moreover, the iron and chromium diffuse into one another, forming an iron-chromium alloy shell thereby giving the core/alloy product an interface similar to some forms of stainless steel.

Since stainless steel is known for its resistance to oxidation, the big challenge for Maye and Wu has been finding out how nanoparticles cope during this process.

‘We’ve discovered that nanoparticles exhibit a unique behaviour when oxidized,’ he said. ‘A thin, iron-chromium oxide shell forms, leaving behind an unoxidised iron core. Even more interesting is the fact that a void forms, separating the core from the shell.’

Although core/alloy fabrication is a new approach, it may allow for more diverse forms of alloy nanomaterials.

‘Most alloys we take for granted at the macroscale, such as steel, are hard to fabricate at the nanoscale, because of ease of oxidation and other specific conditions that are required,’ said Maye. ‘Our approach may open new doors.’