This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Rice University researchers have developed a way to stabilize diamond during high-temperature and low-pressure processing, creating a strong bulk composite and discovering that high-speed collisions can rapidly transform diamond into graphite. Their study is published in Materials Today.
Diamond is one of the hardest known materials, with high thermal conductivity, properties that make it valuable for technologies that operate under extreme conditions. The findings could help researchers design tougher materials for aerospace, defense and other demanding environments by showing how diamond changes and absorbs energy under extreme force. "This was quite an exciting outcome as it is nearly impossible to sinter diamond at lower pressures, and this new process we have developed could lead to the large-scale manufacturing of diamond-based composites," said Pulickel Ajayan, the lead author of the study and the Benjamin M. and Mary Greenwood Anderson Professor of Engineering.
Small diamond particles are relatively inexpensive and easy to produce, but turning them into larger diamond structures has proved difficult, Ajayan said. One way to join those particles into a larger structure is through sintering, a process that uses heat and pressure to form a solid. With diamond, however, the high temperatures can turn it into graphite.
High-pressure, high-temperature methods can produce polycrystalline diamond, but they require extreme pressure and limit the size of the samples produced. To keep diamond stable during processing, the researchers mixed microscopic diamond grains with cubic boron nitride, a material with properties similar to diamond, and cobalt to bind and stabilize the mixture. They used spark plasma sintering, a rapid process that applies heat and pressure to turn powders into a solid.
The process produced an extremely strong composite with diamond particles embedded in the boron nitride matrix and cobalt distributed throughout. "The composite made by this process is almost nonmachinable and tough due to the presence of dispersed diamond particles and could help researchers design tougher materials for aerospace, defense and other technologies that face extreme conditions," said Abhijit Biswas, the first author and a research scientist in Rice's materials science and nanoengineering department. The researchers then subjected the composite to high-speed collisions to study how it behaved under extreme force.
Researchers fired tiny metal projectiles measuring 1–4 millimeters (0.04–0.16 inches) across at the composite at hypersonic speeds, and the material held together when struck by one of the projectiles traveling at more than seven times the speed of sound. A larger projectile traveling even faster caused the composite to break apart. During the collision, nearly all the diamonds involved in the transformation became graphite within microseconds.
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