Safety coating causes heat-damaged ropes to change color
When a rope is heated – either by friction or by fire – it may lose its structural integrity, subsequently breaking when put under load. A new surface coating, however, could cause ropes to change color if they've been overheated, providing a warning to users.
The technology builds upon a color-changing coating previously developed by Switzerland's ETH Zurich and Empa research groups. Originally, that coating could only be applied to flat surfaces. Now, Empa has modified it to also work on curved surfaces such as rope fibers.
The coating is applied to ropes in three layers, utilizing a process known as sputtering. Its first layer – the base – consists of silver, which reflects incoming light. Applied next is a layer of titanium nitrogen oxide, to stabilize the silver. Finally, a layer of germanium-antimony tellurium is applied on top.
When the latter chemical is subjected to high temperatures, it crystallizes, permanently changing color from blue to white. The silver base of the coating makes that color-change easier to see.
By tweaking the composition of the germanium-antimony tellurium, it's possible to move the temperature at which it crystallizes, within a range of 100º to 400º C (212º to 752º F). This adjustability could certainly come in handy, as different rope materials lose their integrity at different temperatures. For the experiments, a polyester/Vectran filament was used, with a coating that was tuned to turn white at 150º C (302º F).
Unfortunately, the present version of the coating oxidizes within a few months, losing its functionality in the process. It is hoped that once this hurdle has been overcome, the technology could find use on ropes utilized by people such as firefighters, mountain climbers, rescue teams, or construction workers.