Why diamonds can be ground at all
29. November 2010, 17:28 Why can not at all polished diamonds have now scientists from the Fraunhofer Institute for Mechanics of Materials IWM in Freiburg found.
Researchers decipher atomic mechanism of the diamond processing: A "glass-like carbon phase" makes it possible
Freiburg - It is the hardest material in the world, and yet can grind diamond itself. Already 600 years ago were first diamond cut and the precious stones were quick to most expensive jewelry, and later became indispensable industrial tool. Now a team led by Lars Pastewka and Michael Moseler from the Fraunhofer Institute for Mechanics of Materials IWM in Freiburg has revealed the secret of why diamond can work at all.
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The research findings represent a major step in tribology, ie the friction and wear research, which is now understood despite its importance for the industry to its scientific basis is still largely.
For centuries, diamonds are cut by skilled craftsmen in a Cast iron wheel, which is peppered with fine diamond chips and fast, with tip speeds of about 30 meters per second, rotating. At the sound of the grinding wheel and with their proverbial tact recognized by experienced diamond cutter, like they have to keep the diamond in the rough to smooth it and to get a polished surface before they can enter the diamond trade for sale. .
No more diamond
That diamond reacts depending on the direction, has long been known. Physically, the phenomenon is called anisotropy. The carbon atoms in diamond lattice planes and shapes depending on how you turn the diamond, with one from levels that are easier or harder to polish.
For centuries, scientists are looking for a plausible explanation of this empirically proven Anistropie - so far without success. Nor could now be explained, how can it be that the hardest material can be processed at all. The Freiburg scientists have now answered both questions with a newly developed computational method. The result of Michael Moser brings so to the point: "The moment in which the diamond is cut, the diamond diamond no more."
New "glass-like carbon phase"
In a mechano-chemical processes - by the rapid friction between the diamond chips in Cast iron wheel and the rough diamonds to be polished - a completely different "glass-like carbon phase" on the gemstone surface. How quickly this occurs material phase depends crucially on the crystal orientation of the rough diamonds. "Right here that is said anisotropy comes into play," said Moser.
The newly formed material on the diamond surface, Moselle, in the end in two ways "peeled off": The plane effect of the sharp-edged diamond chips in the wheel scratch continuously from small carbon dust particles from the surface, which in its original state it would not be possible because of the diamond too hard and the binding forces would therefore be too high. The second, equally significant attack on the otherwise impenetrable hard crystal surface, the oxygen does in the air. Meanwhile, O2 molecules bind one carbon atom from the unstable, long carbon chains that have formed on top of the glassy phase: The result is carbon dioxide.
And how could calculate when and how individual atoms are dissolved from the crystalline surface? "Was essential if we took a look at exactly what happens quantum mechanically, when a bond breaks between the atoms on the surface of rough diamonds. We have analyzed the particular field of force between the atoms exactly," said Lars Pastewka.
Exact model
Know these forces accurately enough, one could arise and the breaking of the new chemical bonds between the atoms accurately describe - and model. "And on this basis, we have studied the dynamics of atoms in the friction between a diamond and precious stone chips," adds Pastewka. To this end, he and his colleagues, the paths of about 10,000 carbon atoms calculated and is monitoring the screen. Their equation was: Your model can explain all the processes of long opaque diamond polishing.
The model is not only a milestone in the diamond research, "it demonstrates much more are also using modern methods of materials modeling, friction and wear processes on the atomic level to the macroscopic object can be described accurately," says institute director Peter Gumbsch. He sees this as an example of the plurality of wear issues in the industry is still waiting for a solution. This will turn to the Fraunhofer IWM in his Mikrotribologiezentrum μTC under the motto: "Tribology make predictable. His knowledge makes the team in the current online issue of Nature Materials to the public.
