In this article, we will answer the following question: “Is Aerogel Flammable?”, and other important questions about aerogel materials, focusing especially on aerogel insulation composites.
Is Aerogel Flammable?
The quickest answer is: probably not. Aerogel materials are normally composed to prevent fire hazards. But keep in mind that aerogels are a class of materials, with hundreds of applications.
An aerogel could be flammable depending on the materials added to it.
What is aerogel?
Aerogel is an ultralight material derived from a gel. It can be made out of clay, polymers, metal oxides, and silica.
It’s also known by the nicknames: “frozen smoke”, “pet cloud”, “solid smoke”, and “solid cloud”.
Graphene aerogel (aerographene) is considered to be the world’s lightest solid material.
Imagine a gel structure where the liquid part had been exchanged with air, leaving a porous structure in a solid material. That’s essentially what aerogels are.
The resulting material is so light that more than 99% can be made of air. The resulting material tends to be fragile in its pure version, but commercial aerogel materials are composed of other things as well, so their physical properties are wide.
More scientific characteristics will be discussed in the following topics.
What is it used for?
Aerogels can be used for many things, we are just beginning to use them. Here’s a small list of some applications:
- Domestic thermal insulation: due to its low thermal conductivity, aerogels are used as insulators inside walls and roofs because they can prevent heat from spreading in or out. This same condition helps prevent itself from catching fire.
- Aerospace insulation: it can be used as a thermal insulator in space suits and space crafts.
- Electronics: they can be used to create supercapacitors, which can lead to new battery technologies.
- Cosmic dust collecting: NASA has used silica aerogel to trap cosmic stardust, using a probe. The porous silica structure allowed it to serve as a fishing net but instead of fish, it captured stardust.
- Rackets: Dunlop Sports has used aerogel in some of its racquets.
- Aerogels made from chalcogenide (a chemical compound) can be used in water treatment to absorb heavy metals.
- Nanotechnology: due to the porosity arising in a nanoscale, many technologies arise from aerogel.
- Oil absorption: Aerogel could be used to absorb petroleum in oil spills, for example.
Combustible insulation materials have been at the center of domestic fire hazards for many years.
These materials are used because of their thermal insulation properties, which maintain the heat inside a home or a business when is cold while keeping the heat outside when is hot.
Normally the materials used are polyurethane foam or expanded polystyrene, which are very light and little dense kinds of plastic because the materials are made with a lot of air inside.
Imagine a thermal box or a thermos flask. The reason why they can keep our provisions cold or heated is that their materials are thermal insulators, which means that the heat can’t find an easy way to escape. More will be discussed in the rest of this article.
What is it made of?
Most of its volume is air. An aerogel can have many matrixes.
The forming element “aero” in aerogel comes from the Greek word “aeros”, which means air.
In insulation materials, the aerogel is a composite made by mixing glass with a polymer.
The top 3 characteristics aerogel has are low thermal conductivity, hydrophobicity (hard to get moist), and low flammability.
At the same time, every aerogel is unique. Each one has its own set of properties. We can never assume a certain material has an extreme behavior judging by its general characteristics.
In this video, you can see a flamethrower being used against a fiberglass blanket which was infused with silica aerogel.
Source: Flamethrower vs Aerogel
The thermal conductivity of aerogel materials is really low. Silica itself is not a good heat conductor, and so is the air.
Make no mistake: aerogels can burn, especially if they have an organic compound mixed. But, indeed, even these shouldn’t ignite under normal circumstances.
So why don’t scientists and engineers use only non-flammable matrixes to create aerogels?
The answer to this relies on the properties that industries require, and the means the composites are used for.
A silica-based aerogel, for example, can be really light, translucid, pretty, and seem very useful, but it’s also friable and solid-like. Polymer-based aerogels tend to be much more foam-like and present more malleability.
But the more a polymer is added to create an aerogel, the more flammable it is. The right portion of each material used to create an aerogel could take years to develop.
Aerogels are often treated chemically so water can’t penetrate their surface. This capability is very useful, especially for insulation purposes, so it can also prevent moisture and mold.
To avoid fires we must first understand how they happen.
Fire is the result of a chemical reaction between a source of an organic compound and oxygen gas. The second ingredient is normally available everywhere on our planet, so we must make sure that the first one isn’t.
An organic compound is made mostly of carbon and hydrogen. At least at some point, all organic matter is derived from life. So fire was only possible after life began on our planet.
A combustion reaction takes place when a source of organic molecules can interact with oxygen after an ignition, so carbon can be oxidized until becomes carbon dioxide (CO2). Hydrogen, in its turn, also interacts with oxygen and ends up producing water (H2O).
Heat is also an important part of combustion. It allows oxygen to be available so the reaction can go on.
Many aerogel compounds do not use an organic matrix, so they can’t possibly burn. Because of their low thermal conductivity, they can’t even be heated, and that’s why they’re used in many things.
But what about polymer aerogels?
So, we already know that polymers can burn, they can serve as fuel in a fire. At the same time, characteristics such as malleability are required for many industries, so polymers must be applied in certain aerogels.
This review showed that aerogels can be flammable, but not normally. Also, they tend to be much less flammable than other products that have similar uses.
Every new aerogel product must have its flammability properties assessed individually, we can’t be certain judging only by similar products.
But if you possess a certified product from a known brand and it specifically says that it is not flammable, the safety trials have already happened and you should trust the label.
Aerogel is normally not flammable. It presents very good thermal insulation properties and can be used for many things. Its characteristics make it a great non-flammable thermal insulant.
Frequently asked questions: “Is Aerogel Flammable?”
Is Aerogel biodegradable?
Sometimes. It depends on the product. An aerogel could be composed using biodegradable materials but even so, doesn’t present biodegradability. This happens because a new material is being composed, and nature may not be ready to degrade it yet.
Is aerogel harmful to humans?
Any licensed product had undergone extensive safety trials before being commercially available, so it should be safe. Fabricant instructions should always be followed.
How much heat aerogel can handle?
It depends on the product. There are aerogel products that can burn but at a much slower pace. But others could sustain extreme heating, more than we can provide at home.
Can I make aerogel from home?
No. This substance requires specific synthetizing which includes severe low temperatures that can’t be achieved from home.
Hong-Bing Chen & David A. Schiraldi (2019) Flammability of Polymer/Clay Aerogel Composites: An Overview, Polymer Reviews, 59:1, 1-24, DOI: 10.1080/15583724.2018.1450756