For rescue personnel, construction workers, or climbers, a rope is often a lifeline. However, it is a vulnerable link in the safety chain: Excessive heat weakens ropes increasing the risk that they could snap during future use.

For this reason, a team of researchers at the Swiss Federal Laboratories for Materials Testing and Research (Empa) has developed a warning system for fibers. The coating is applied to ropes and consists of the three layers silver, titanium-nitric oxide, and an ultra-thin and temperature-sensitive layer composed of the elements germanium, antimony, and tellurium. This top layer, which is only a few nanometers thick, crystallizes at high temperatures and changes its color from blue to whitish, as the researchers were able to demonstrate in a heat test at 150 degrees. For firefighters, for example, white would mean that a rope no longer offers the desired level of safety for future missions.

Durability not yet guaranteed

According to a statement issued by Empa, the coating could be adapted for the color change to take place at temperatures ranging between 100 and 400 degrees Celsius by changing the chemical composition of the top layer. Currently, however, the coating loses its properties over time, since the materials oxidize and the top layer loses its ability to crystallize. Thus, further research will focus on increasing the durability of the coating.