Science News
from research organizations

How to soften a diamond

January 6, 2011
After hundreds of years, researchers have managed to decode the atomic mechanism behind diamond grinding.

Material removal mechanism during diamond polishing: a sharp-edged diamond particle “peels off” a dust particle from the glass-like phase at the surface of the diamond. At the same time, oxygen from the air reacts with the carbon chains at the surface to form carbon dioxide.
Credit: Image courtesy of Fraunhofer-Gesellschaft





Michael Moseler explains the method in layman's terms: "The moment a diamond is ground, it is no longer a diamond." Due to the high-speed friction between the rough diamond and the diamond particles in the cast iron wheel, a completely different "glass-like carbon phase" is created on the surface of the precious stone in a mechanochemical process. The speed at which this material phase appears depends on the crystal orientation of the rough diamond. "This is where anisotropy comes in," explains Moseler.

The new material on the surface of the diamond, adds Moseler, is then "peeled off" in two ways: the ploughing effect of the sharp-edged diamond particles in the wheel repeatedly scratches off tiny carbon dust particles from the surface -- this would not be possible in the original diamond state, which is too hard and in which the bond forces would be too great. The second, equally important impingement on the normally impenetrably hard crystal surface is due to oxygen (O) in the air. The O2 molecules bond with carbon atoms (C) within the instable, long carbon chains that have formed on the surface of the glassy phase to produce the atmospheric gas CO2, carbon dioxide.

And how was it possible to determine when and which atoms would detach from the crystalline surface? "We looked extremely closely at the quantum mechanics of the bonds between the atoms at the surface of the rough diamond breaking. We had to analyze the force field between the atoms in detail," explains Lars Pastewka.

If one understands these forces well enough, one can precisely describe -- and model -- how to make and break bonds. "This provided the basis for investigations into the dynamics of the atoms at the friction surface between a diamond particle on the wheel and the rough diamond itself," adds Pastewka. He and his colleague Moseler have calculated the paths of around 10,000 diamond atoms and followed them on screen. Their calculations paid off: their model is able to explain all the processes involved in the dusty and long misunderstood method of diamond grinding.

The newly developed model is not only a milestone in the field of diamond research: "It proves also that friction and wear processes can be described precisely with modern material simulation methods ranging from the atomic level to macroscopic objects." emphasizes Prof. Peter Gumbsch, director of the institute. He considers this just as one example of the many questions on wear that industry needs answers to. These questions will be addressed in future by the Fraunhofer IWM within the newly founded MicroTribology Centre µTC under the motto "make tribology predictable."

Story Source:


Journal Reference:

  1. Lars Pastewka, Stefan Moser, Peter Gumbsch, Michael Moseler. Anisotropic mechanical amorphization drives wear in diamond. Nature Materials, 2010; DOI: 10.1038/nmat2902

Cite This Page:

Fraunhofer-Gesellschaft. "How to soften a diamond." ScienceDaily. ScienceDaily, 6 January 2011. <>.
Fraunhofer-Gesellschaft. (2011, January 6). How to soften a diamond. ScienceDaily. Retrieved May 28, 2015 from
Fraunhofer-Gesellschaft. "How to soften a diamond." ScienceDaily. (accessed May 28, 2015).

Share This Page: