Is CARBON Hard or Soft?

   
  Diamonds are made of carbon. They are among the hardest of materials and are used to cut glass and steel. Graphite is also a form of the element carbon. It rubs off easily on paper, which is why we use it to make pencil leads.

If diamonds and graphite are made out of the same element, why do they look so different and behave so differently? Take a closer look:

Above is a drawing of the crystalline structure of a diamond. The spheres represent carbon atoms; the lines connecting the atoms represent chemical bonds. Each carbon atom is at the center of a four-sided pyramid, or tetrahedron, formed by the neighboring carbon atoms to which it is bonded.

Above is a drawing of a graphite crystal. A few carbon atoms are bonded vertically to those above and below, but most are only attached to neighbors in the same horizontal plane.

Do these drawings suggest a reason why diamonds are hard while graphite breaks apart easily? The answer has to do with how the carbon is arranged in the two materials--with the materials' structures.

Click here to try an activity that explores this idea further:

                                  
Materials scientists are interested in knowing how a material's macroscopic properties-- such as hardness, resistance to extreme temperatures, electrical conductivity, and many others--are related to its atomic structure. This knowledge can be used to improve materials and develop new materials to meet specific needs.

For instance, materials scientists at Lawrence Berkeley National Laboratory recently invented a new material that is harder than diamonds. It may be used as an inexpensive substitute for diamonds or to carve diamonds into intricate shapes for use in electronic devices. Scientists are also experimenting with a recently discovered carbon structure, called buckminsterfullerene (or fullerene for short, or "buckyballs" for shorter) that looks like this:

                              
The buckyball is named after Buckminster Fuller, the inventor of the geodesic dome. One of the many interesting qualities of buckyballs is that atoms of other elements can be put inside the buckyball "cage," creating all sorts of possibilities for new materials.

Studying a material's structure often means looking at its atomic structure--how its atoms fit together and interact. The ALS allows scientists to study materials on the scale of their atomic structure.

To find out how researchers are using the ALS to study materials, just click on one of the following:

Kevlar--The Wonder Material

Selenium: A Window On Wetlands

   
 

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