CSIRO researchers have discovered strange diamonds from an ancient planet in our solar system could hold the key to making stronger and harder machine parts. Mignon D’Souza caught up with CSIRO researcher Colin MacRae to find out more about the project.
For a few years now, scientists at CSIRO have been working on a project to confirm the existence of a mineral known as lonsdaleite.
Lonsdaleite is a rare, hexagonal-shaped diamond believed to be found in ureilite meteorites from the dwarf planet’s mantle.
The project team – with scientists from Monash University, RMIT University, CSIRO, the Australian Synchrotron and Plymouth University – recently found evidence of how lonsdaleite is formed in the meteorites, thus confirming its existence.
The findings of the study – led by geologist Professor Andy Tomkins from Monash University – have been published in the Proceedings of the National Academy of Sciences (PNAS) journal.
Researchers have revealed a novel process in which the lonsdaleite is created, replacing graphite crystals in the dwarf planet’s mantle facilitated by a super-hot fluid as it cools and decompresses.
“We propose that lonsdaleite in the meteorites formed from a supercritical fluid at high temperature and moderate pressures, almost perfectly preserving the textures of the pre-existing graphite,” Professor Tomkins said.
“Later, lonsdaleite was partially replaced by diamond as the environment cooled and the pressure decreased.”
All of this sounds very scientific, but the discovery has extraordinary potential for the making of machine parts.
Professor Dougal McCulloch, director of the RMIT Microscopy and Microanalysis Facility and one of the senior researchers on the team, said the team predicted the hexagonal structure of lonsdaleite’s atoms made it potentially harder than regular diamonds, which have a cubic structure.
CSIRO scientist Mr Colin MacRae added that this is a potential breakthrough for manufacturing machine parts.
“This process isn’t normally possible because when you convert carbonaceous material through to diamond, it’s in a very high-pressure medium where you can’t easily control the shape – you just jam everything together. Whereas here, the graphite is being transformed through to an ultra-hard material,” MacRae said.
The study used a range of cutting- edge science techniques on the largest sample of ureilite meteorites to date. At CSIRO, an electron probe microanalyser (EPMA) was used to quickly map the relative distribution of graphite, diamond, and lonsdaleite in the samples.
This instrument, together with high-resolution transmission electron microscopy (TEM) at RMIT University, helped identify the largest lonsdaleite crystallites to date – up to one micron in size.
Dougal McCulloch and his RMIT team, PhD scholar Alan Salek and Dr Matthew Field, used advanced electron microscopy techniques to capture solid and intact slices from the meteorites to create snapshots of how lonsdaleite and regular diamonds formed.
Professor Tomkins of Monash University said the study findings helped address a long-standing mystery regarding the formation of the carbon phases in ureilites.
“Nature has thus provided us with a process to try and replicate in industry. We think that lonsdaleite could be used to make tiny, ultra-hard machine parts if we can develop an industrial process that promotes replacement of pre- shaped graphite parts by lonsdaleite,” he explained.
Collin MacRae reinforced why the discovery was very exciting for industry – the unusual structure of lonsdaleite can help inform new manufacturing techniques for ultra-hard materials in mining applications.
“We often see graphite associated with these diamonds. What’s really interesting for us, is that the lonsdaleite texture looks like it has the texture of graphite, which indicates very strongly that the formation processes simply allowed the atoms to transition from a graphite structure through to a long starlight structure,” MacRae explained.
“It’s exciting because it means that potentially if you understand how to produce this material in the laboratory, which is supposedly harder than normal diamond, you could actually shape the graphite and convert it to limestone light and end up with shapes and materials.”
Collaboration is key
CSIRO’s Dr Nick Wilson said the collaboration of technology and expertise from the various institutions involved allowed the team to confirm the lonsdaleite with confidence.
“At CSIRO, an electron probe microanalyser was used to quickly map the relative distribution of graphite, diamond and lonsdaleite in the samples. Individually, each of these techniques give us a good idea of what this material is, but taken together – that’s really the gold standard,” he said.
To purchase a new cutting-edge electron microscope, CSIRO received special dispensation from the Australian Research Council (ARC) because the organisation has experts in that type of microscopy, with the ability to operate the equipment in-house.
Colin MacRae explained CSIRO’s proficiency in this space. “Our interest is in alternative materials for cutting materials for mining. That’s the reason why we’re interested in alternative materials like this.
“And so, we were completely supportive of analysing this problem with any company and we can see that potentially further down the track, we might end up with something that advances some mineral processing, exploration and similar areas.”
“I’m an electron microscopist with a special interest in cathodoluminescence and software threat analysis,” MacRae explained his role in the project. “And that’s a unique capability that we’ve developed here over the last 15 to 20 years. We’re world experts in that area, and we’ve developed unique spectrometry and analytical techniques in that area.
“That proved to be through finding lonsdaleite. Because of lonsdaleite’s structure, there is a very strong image of luminescence when you struggle with an electron beam and so having cathodoluminescence, at least spectroscopy, has been the reason why we’re able to do this research.”
On the involvement of other partner universities and their collaborative efforts, MacRae said they had already been collaborating with Monash University and RMIT previously.
“In Scotland three years ago, we used advanced techniques that we’ve developed using this new microscope to find samples of lonsdaleite. We took some samples to RMIT to Dougal McCulloch’s laboratory,” he explained.
“And they are world experts in carbon transmission electron microscopy – carbonaceous materials.
Dougal has a lot of knowledge about how to make countermeasures materials as well. And so, he proved beyond any doubt that what we were looking at was, in fact, a one-star light structure as opposed to a simple diamond structure. That’s how the collaborations came about.”
Industrial applications for lonsdaleite
Lonsdaleite’s discovery can now lead to its synthetic production, in the same way cubic diamonds are grown for use in industries like mining. Since lonsdaleite is much harder than a regular diamond, it can be used to create more durable machine parts.
Lonsdaleite has an added benefit according to MacRae, appearing to require lower pressures than its cubic cousin.
“If something that’s harder than diamond can be manufactured, that’s something industry would want to know about,” he said.
“Mining is one of the big areas for ultra-hard materials, where they can be used for cutting rocks. And so normally, these materials are fused diamonds in a silicon carbide matrix, and they do wear out. Therefore, we need to produce something that’s got harder materials than it’s going to wear. And it’s just going to be more efficient to operate them as well.
“Applications for mining are quite extensive. They could be useful for drilling nitrite. But certainly, the big application that we’re looking at is for the mining industry. That’s an exciting area for us.”