New formula can turn cement into metal
"This new material has lots of applications, including as thin-film resistors used in liquid-crystal displays, basically the flat panel computer monitor that you are probably reading this from at the moment," said Chris Benmore, a physicist from the US Department of Energy's (DOE) Argonne National Laboratory who worked with a team of scientists from Japan, Finland and Germany.
Benmore and Shinji Kohara from Japan Synchrotron Radiation Research Institute/SPring-8 led the research effort. This change demonstrates a unique way to make metallic-glass material, which has positive attributes including better resistance to corrosion than traditional metal, less brittleness than traditional glass, conductivity, low energy loss in magnetic fields, and fluidity for ease of processing and moulding.
Previously, only metals have been able to transition to a metallic-glass form. Cement does this by a process called electron trapping, a phenomena only previously seen in ammonia solutions. Understanding how cement joined this exclusive club opens the possibility of turning other solid normally insulating materials into room-temperature semiconductors.
"This phenomenon of trapping electrons and turning liquid cement into liquid metal was found recently, but not explained in detail until now," Benmore said. "Now that we know the conditions needed to create trapped electrons in materials we can develop and test other materials to find out if we can make them conduct electricity in this way," Benmore added.
The team of scientists studied mayenite, a component of alumina cement made of calcium and aluminum oxides. They melted it at temperatures of 2,000 degrees celsius using an aerodynamic levitator with carbon dioxide laser beam heating. The material was processed in different atmospheres to control the way that oxygen bonds in the resulting glass. The levitator keeps the hot liquid from touching any container surfaces and forming crystals.
This let the liquid cool into glassy state that can trap electrons in the way needed for electronic conduction. The levitation method was developed specifically for insitu measurement at Argonne's Advanced Photon Source by a team led by Benmore.
The scientists discovered that the conductivity was created when the free electrons were "trapped" in the cage-like structures that form in the glass. The trapped of electrons provided a mechanism for conductivity similar to the mechanism that occurs in metals.
The results were published in the journal the Proceeding of the National Academy of Sciences.