Moscow Institute of Physics and Technology

Physicists just 'undiscovered' an important metal compound

The scientific method in action.

FIONA MACDONALD
29 MAR 2016
 

Physicists have demonstrated that a controversial but much-hyped compound, known as technetium carbide, doesn't actually exist, despite earlier evidence to the contrary. 

That might sound like a whole lot of words that aren't relevant to your life in the slightest, but it's actually a big deal, because carbide compounds look like they're going to be incredibly useful for a range of industries. Think coatings that make tools cut better, or speed up chemical reactions - we just need to figure out how they work first. And this latest discovery is a big step in the right direction.

 

So let's take a step back for a second, because if you're anything like us, you're sitting there wondering what the hell is technetium, and what are carbides?

Technetium is a transition metal with an atomic number of 43 on the periodic table, and it's got no stable isotopes, which means that every form of it is radioactive.

Transition metals are elements that can form bonds through electrons sitting in their d-orbital, such as iron and copper. But unlike those more common elements, technetium is incredibly rare in nature and is pretty much only ever synthesised in the lab.

That's interesting enough on its own, but when a transition metal bonds to carbon, they form what's known as carbides - and that's fascinating to a whole lot of people, because carbides are incredibly hard, heat-resistant substances.

So engineers think these substances are probably going to be great coatings for cutting tools, and chemists are also interested in them, because they have catalyst abilities similar to expensive platinum plates - except they're a whole lot cheaper.

That's all great, but we still don't know a whole lot about these transition metal carbides, which is why it was so exciting when, a few years ago, a team claimed they'd synthesised technetium carbide. The claim was met with controversy, but no one had been able to conclusively prove whether or not the compound existed.

 

Now a team from the Moscow Institute of Physics and Technology in Russia has used an algorithm to model a whole range of potential transition metal carbides for the first time, and has demonstrated that technetium carbide is impossible.

They were able to do this by calculating two key parameters for each potential carbide: the energy of metal atoms’ bonding, and the energy required to insert carbon into the lattice of metal atoms.

Basically, if the energy required to insert carbon into the lattice is too great, then a carbide is unstable and can't be formed - and that's the case for technetium.

So why did researchers think technetium carbide was possible in the first place? The earlier evidence was seen in powder X-ray diffraction patterns, with two characteristic peaks. However, when the Russian team modelled the X-ray scattering process in pure technetium, they saw a very similar picture, and even better matching experimental data.

"Therefore, the previous group might have mistakenly assumed the pure element's trace for that of technetium carbide," the researchers report.

This study isn't only important because it 'undiscovered' a compound - it also paves the way for future research on transitional metal carbide prospects, and puts in place a system we can use in future to identify which ones are worth looking into.

"In this paper we added a modicum of clarity as to the causes of the formation of these compounds, and created a foundation for future research and quest for new carbides useful in practical applications," says co-author Oleg Feya. "Besides, sometimes an 'undiscovery' of a substance such as [technetium carbide] at the right moment can help save time and efforts of contemporary and future researchers in the field."

The research has been published in RSC Advances.

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