A team of researchers based at Yanshan University has produced a new synthetic diamond that’s remarkably robust, outperforming natural diamonds and other synthetic diamonds in both thermal stability and pressure tests. The results have been published in Nature.
Diamond is the hardest natural material known to man and consequently it is used in a wide variety of industrial settings such as aerospace engineering, mining and car manufacture. Its hardness and wear resistance makes it a particularly useful material for cutting tools but unfortunately poor stability at very high temperatures has restricted its applications in industry. Researchers are therefore turning to synthetic diamonds in order to overcome the limits of natural diamonds.
In nature, diamond occurs only as single crystals and while these materials are pretty hardy, they’re expensive and tend to wear unevenly. Synthetic diamonds, however, can either be prepared as single crystals or as a polycrystalline or nanocrystalline material. Polycrystalline diamond (PCD) is formed from tiny grains of diamond, as small as tens of nanometers in diameter, which have been fused together under high-pressure, high-temperature conditions. The smaller the grain, the harder the diamond.
These diamonds offer numerous benefits over natural diamonds given reduced costs, improved hardness and high wear resistance. However, industry is pushing these diamonds to the limits and there has been a need to develop even better diamonds.
In order to produce their super-hard diamond, the researchers subjected carbon nanoparticles that were layered like onions to high pressures and temperatures. The grains were arranged in pairs that were a mere 5 nanometers in size. The resulting “nanotwinned” diamond demonstrated remarkable thermal stability and hardness.
The team applied large pressures to the diamond and found that it was able to endure pressures of up to 200 gigapascals, which is around 1.9 million atmospheres. It would take only around half that pressure to shatter a natural diamond.
Next, they tested temperature resistance by investigating the highest temperature that could be tolerated before the diamond started to oxidize. They found the synthetic started to oxidize at temperatures between 980-1,056oC (1,796-1,932oF), which is around 200oC higher than that of natural diamond.
The researchers hope that this method could be adopted in industry as a way to produce novel carbon-based materials that are super-hard and exceptionally heat stable.