Scientists fabricate first highly oxidation-resistant boride

26th May 2016

Enaie Azambuja

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Borides are among the hardest and most heat-resistant substances on the planet, but their Achilles' Heel, like so many materials', is that they oxidise at high temperatures. Oxidation is the chemical reaction commonly known as corrosion or rusting - it can signal the end for a material's structural integrity. But researchers from Drexel University, Linkoping University in Sweden and Imperial College London have produced an aluminum-layered boride whose unique behavior at high temperatures keeps it one step ahead of nature's slow march toward high- temperature chemical degradation.

So impressive is their perceived durability, that borides are used as coatings for surfaces that must survive the harshest environments - from the inside of combustion engines to cutting tools for hard metals.

But, according to Michel Barsoum, PhD, distinguished professor in Drexel's College of Engineering who is the lead author of research recently published in Scientific Reports, we can make borides better.

"This discovery is quite significant because it is the first example in the history of humankind of a transition metal boride that is quite oxidation resistant," said Barsoum, who heads Drexel's MAX/MXene Research Group in the Department of Materials Science and Engineering.

To make their boride material, called molybdenum aluminum boride (MoAlB), Barsoum and his team combined a molybdenum-boron lattice with a double layer of aluminum to produce a material that is durable enough to resist oxidation at extremely high temperatures.

The key to this remarkable characteristic is the material's nanolaminated structure with alternating layers of molybdenum boride and aluminum - a form the Drexel group has established a reputation for working with since its creation of MAX phases two decades ago.

Upon testing, the group also found that the material retains its high conductivity to elevated temperatures. Its melting point has yet to be determined, but preliminary results have shown it to be greater than 1400ºC.