Nanodiamonds Witnessed Forming and Decaying
Carbon can take on many forms, and that which most people are likely interested in are diamonds, prompting many sayings to be made about them. One of these is that diamonds are forever, but in reality, diamonds are less permanent than most may think. Researchers at Rice University accidentally discovered while studying anthracite coal that they were creating nanodiamonds, and watched as they decayed back into graphite.
The original purpose of the research was to find ways to reduce the carbon in the anthracite coal and make it soluble. This work required placing samples under an electron microscope. As it turns out, the microscope's electron beam had enough energy to cause an unpredicted reaction. The carbon in the coal was bonded to hydrogen, but the electron beam had enough energy to break those rather strong bonds. Suddenly without the hydrogen atoms, the carbon atoms started bonding with each other, forming a structure similar to nanodiamonds, until the pressure stopped the process. As the researchers kept the electron beam going, they watched as the nanodiamonds decayed, in part because of the energy from the beam, but also because of their small size.
With help from the Technological Institute for Superhard and Novel Carbon Materials in Moscow, the researchers created a phase diagram for nanodiamonds, which indicates how one might make nanodiamonds without the massive pressures normally used. The diagram also indicates that there is a window of stability, in which the diamonds would not decay back into anthracite, potentially allowing them be put to some use.
Source: Rice University