The diamond is the hardest material in the world. But why does the crystal of carbon grind nonetheless valuable gems? Quantum physicists have now found out a surprising answer: the carbon atoms are "liquid".
A team of German researchers has discovered why diamonds - can grind at all - after all, the hardest material in the world: When polishing its surface is soft, so to speak. It is formed between the stone and the diamond chips of the grinding wheel, a layer in which the individual carbon atoms are much less tightly bound together than in the crystal itself, this layer can then either be mechanically using the disk or removed chemically by the action of atmospheric oxygen . "The moment in which the diamond is cut, the diamond is not a diamond more," Michael Moser brings the Fraunhofer Institute for Mechanics of Materials in Freiburg, the results of the study to the point.
The researchers were able to show that using complex calculations, in which they simulated the quantum-mechanical behavior of individual carbon atoms. Thanks to this procedure will be answered in future also other previously unresolved questions about friction between solids processes, the team writes to Moser in the journal Nature Materials.
Diamond is because of its extreme hardness in the industry often used as a cutting tool and as a component of polishing paste. But even as he is sought after gem: For centuries grind and polish the rough diamonds to diamonds experienced craftsmen and other forms - with the help of diamond chips on a cast iron disk. However, this sensitivity is called for: A diamond can in fact not the same polish on each side well. Some facets occur easily and are easily smooth and flawless, while others seem to resist the grinding. In such places can be very difficult to generate high-quality surfaces. Scientists have been looking for an explanation for this phenomenon - as a response to the much more fundamental question of why the surface of the hard diamond ever respond to treatment with fragments of the same material, which is so sought after buy diamond buyers from all over the world.
Moser and his colleagues have now developed a new computational method that they could determine exactly when and how atoms detach from the surface of the diamond. They found that results from the rapid friction between the diamond chips and the uncut diamond grinding a new, less solid carbon layer on the uncut diamonds. In it, the atoms are not strictly arranged in planes as in the crystal, but are rather confused. When polishing the soft layer is then removed in two ways: First, the sharp-edged diamond chips on the grinding scrape out small carbon particles. Second, the oxygen of the air, the carbon atoms to attack the new shift, because their bonds to their neighbors, much weaker than previously in the crystal lattice. Thus, the carbon atoms disappear, so to speak from the solid, because carbon dioxide gas is produced. By the model can also explain the different good polishing results on the various pages of Stone: The soft layer is not everywhere the same speed. Where it occurs rapidly, can easily drag the diamond, and where they are reluctant to buy, the processing is more difficult.
The crucial factor is how the different levels of the diamond crystal are oriented to the grinding wheel. It therefore makes a difference whether the crystal planes are perpendicular to the grinding surface or whether the disc's more like an angle on the crystal surface, the researchers discovered. The model is not only a milestone in the diamond research, says Peter Gumbsch, Director of the Fraunhofer Institute for Mechanics of Materials. It also demonstrates, can be accurately described using modern methods such as friction and wear processes. The question of how it was possible to process diamond is ultimately only one of myriad unresolved issues of material sciences, he stresses.
