A serendipitous discovery at Stanford revealed the properties of a material that changes form when exposed to flame. The finding holds promise for a spray coating that could protect homes from fire over four times as long as current solutions.
In 2019 a team of Stanford University researchers, led by materials science and engineering professor Eric Appel, developed a hydrogel that could be applied to vegetation to give them long-lasting protection from wildfires. In a new study, after years of refining the material, Appel and his team decided to see if the gel could offer similar protection to wooden structures and if so, how.
In lab tests, the researchers found that indeed it could. The reason was that after all of the liquid in the water-rich hydrogel burned away, the remaining silica in the compound arranged it into a strong, porous aerogel foam that could continue to scatter heat and protect the wood beneath it.
“We’ve been working with this platform for years now,” Appel said. “This new development was somewhat serendipitous – we were wondering how these gels would behave on their own, so we just smushed some on a piece of wood and exposed it to flames from a torch we had laying around the lab. What we observed was this super cool outcome where the gels puffed up into an aerogel foam.”
Unlike hydrogels, which are somewhat delicate water-rich gummy substances, aerogels are dry, durable and porous. They've been turned into super-strong transparent bricks, used to harvest water from the air, and formed into the lightest sound-insulating material ever manufactured. Aerogels also have excellent heat-resisting properties so they are often used in applications related to space exploration.
By combining the best of an aerogel with a hydrogel, Appel's team saw impressive results. In tests, the combo gel was able to resist a direct flame for more than seven minutes, as opposed to a currently available fireproofing gel that lasted for less than 90 seconds.
The researchers also say that current fire-resisting gels dry out and become useless about 45 minutes after being applied. With their new material however, because the silica aerogel stays behind until it is washed away, the coating could be applied well in advance of an approaching wildfire while still providing protection when the flames arrive.
“Traditional gels don’t work once they dry out,” Appel said. “Our materials form this silica aerogel when exposed to fire that continues to protect the treated substrates after all the water has evaporated. These materials can be easily washed away once the fire is gone.”
Appel also points out that his gels are environmentally friendly, and composed only of materials that are already approved for use by the US Forestry Service. When eventually washed off, the aerogel is handily broken down by soil microbes.
“They’re safe for both people and the environment,” Appel concluded. “There may need to be additional optimization, but my hope is that we can do pilot-scale application and evaluation of these gels so we can use them to help protect critical infrastructure when a fire comes through.”
The research has been published in the journal Advanced Materials.
Source: Stanford University