A coating that sends a heat warning

At high very temperatures, high-performance fibers tend to lose their mechanical properties. This loss often goes unnoticed and, in the worst case, can cause lifelines to tear when fighting fires, for example. As a result, a research team from the Swiss Federal Laboratories for Materials Science and Technology (Empa) and the Swiss Federal Institute of Technology (ETH) in Zürich have developed a new coating system that will help to prevent this from happening in the future. What makes this possible is that the coating changes its color when it reacts to intense heat and thus shows whether the underlying material is still strong enough to withstand the stress. The change in color is caused by a physical phenomenon known as interference. The coating consists of three layers. A metallic base of silver is first applied to the high- performance fiber. This is followed by a stability-enhancing layer of titanium nitrogen oxide. The final layer is a 20-nanometer-thick application of germanium-antimony-tellurium, or GTS for short. At high temperatures, the GTS crystallizes and the perceived color changes, for example from blue to a whitish hue.