Cement as a semiconductor

Electronics made from cement could be a reality in the future, as scientists from the US, Japan, Finland and Germany unravelled the formula for turning liquid cement into liquid metal.

The researchers demonstrated a unique way to change liquid cement into a metallic-glass material. This material resists corrosion better than traditional metal, is less brittle than traditional glass, is electrically conductive, exhibits low energy loss in magnetic fields, and has the fluidity for ease of processing and moulding.

Previously, only metals have been able to transition to a metallic-glass form. The technique makes cement a semiconductor, allowing its use as thin-film resistors, protective coatings and computer chips.

The discovery is the result of collaboration between the Department of Energy's (DOE) Argonne National Laboratory and the Japan Synchrotron Radiation Research Institute/SPring-8. The results were reported in the journal the Proceeding of the National Academy of Sciences in the article "Network topology for the formation of solvated electrons in binary CaO-Al2O3 composition glasses."

The process by which cement transitions to its metallic-glass form is called electron trapping. While the phenomenon had previously been discovered, the scientists have now identified the detailed conditions required to create trapped electrons in material.

This means they can now develop and test other materials for similar transitions into conductive materials.

To create the metallic-glass material, the scientists melted mayenite, which is a component of alumina cement made of calcium and aluminium oxides, at 2000 degrees Celsius.

The material was levitated and heated with a carbon dioxide laser beam, and processed in different atmospheres to control the oxygen bonds in the resulting glass.

By levitating the molten material, the scientists prevented it from contacting any container surfaces and forming crystals. This led the liquid to cool into a glassy state that can trap electrons, making it conductive.

Through the process, the scientists discovered that conductivity was created when the free electrons were "trapped" in the cage-like structures that form in the glass, giving rise to a similar mechanism for electrical conductivity as found in metals.