Carbon fiber has many advantages, such as light weight and high strength, but it also has some disadvantages. One problem scientists have been struggling with is the oxidation of carbon fibers at high temperatures, and an international team of researchers has now found a low-cost, scalable solution to that problem -- a self-forming protective coating in molten salt.
Thanks to improved manufacturing processes, carbon fiber is already highly heat-resistant and stable in air when temperatures up to 800°C. This makes it ideal for a variety of applications, from bike racks to cars, to medical devices, and even guitars. However, it can run into trouble when it is subjected to extreme temperatures, such as in the aerospace industry. Under these conditions, it reacts with oxygen and burns, resulting in rapid degradation of its structure and excellent properties.
Led by Yongfeng Lu, a research team from the University of Nebraska-Lincoln and the Institute of Condensed Matter Chemistry in Bordeaux, France, tried to solve this problem. "One of the weaknesses of carbon fiber is that if you have a enough high temperature and oxygen, it burns easily," Lu said. If we can make them non-flammable, so that they don't burn when exposed to fire, that would be exciting."
Scientists have made progress in developing more fire-resistant carbon fibers, but these have involved expensive equipment, complicated steps and potentially unpredictable chemical reactions. The authors of the new study have come up with a simple and cheap solution -- start with melted salt.
At 982°C, once the salt crystals have been restored into a liquid, a powder of titanium and chromium is added to the mixture, and then carbon fibre is introduced as a final finish. Due to the different behaviors and reactions of the materials in the molten salt mixture, a chemical reaction is caused to form a protective layer with three different layers.
"We have found a formula that allows three layers of coating in a single impregnation, in a single state," Lu said. The newly coated carbon fiber material was tested in an experimental environment, where the carbon fiber successfully maintained its structure during the entire process under extreme conditions of 1200°C temperature and oxyacetylene torches. A three-layer coating of chromium carbide and titanium carbide was found to provide more protection than a single layer.
"We're trying to add a surface layer that separates carbon fiber from oxygen so it doesn't burn even at high temperatures," Lu said. Carbon fiber can be used in many ways, but if it is flammable, it will introduce new risks to the system and make those applications very limited."
Article source: - China International Composite Materials Industry Technology Exhibition
- cnBetav
Post time: Aug-24-2021