A team of scientists from Japan, Finland and Germany have discovered the formula to turn liquid cement into liquid metal. This makes cement a semi-conductor and opens up its use in the consumer electronics marketplace for thin films, protective coatings and computer chips.
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. 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,” stated Chris Benmore, a physicist from the U.S. Department of Energy's (DOE) Argonne National Laboratory, who along with Shinji Kohara of Japan Synchrotron Radiation Research Institute/SPring-8 led the research effort.
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 C 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 kept the hot liquid from touching any container surfaces and forming crystals, allowing the liquid to cool into a glassy state that could trap electrons in the way needed for electronic conduction. The levitation method was developed specifically for in-situ 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 electrons provided a mechanism for conductivity similar to the mechanism that occurs in metals.
To uncover the details of this process, scientists combined several experimental techniques and analyzed them using a supercomputer. They confirmed the ideas in experiments using different X-ray techniques at Spring 8 in Japan combined with earlier measurements at the Intense Pulsed Neutron Source and the Advanced Photon Source.
The results were reported in Proceedings of the National Academy of Sciences, the official journal of the United States National Academy of Sciences.