AeroGel - The Perfect Home Insulation
"You could take a two- or three-bedroom house, insulate it with aerogel, and you could heat the house with a candle. But eventually the house would become too hot." -- Dr. Peter Tsou of NASA's Jet Propulsion Laboratory once said;
What is an Aerogel?
An aerogel is a manufactured porous solid consisting almost entirely of gas (air) with a very fine latticework of solid material in a spherical shape. This solid material makes up anywhere from five (5%) to one percent (1%) of the volume of the aerogel. Despite the name aerogels do not contain a gel; though they begin life as a material matrix with liquid (gel) supporting the lattice.
Imagine a soap bubble like the ones you played with as a child. Imagine that the bubble has a hard shell rather than the soapy one that only lasts a few minutes at most. If you could save the bubble by giving it a hard shell, you would have a structure that was mostly air, but is very strong in every direction. Additionally, because the bubble is mostly air (or empty space) it takes a while for heat to travel from one side of that bubble to the opposite side.
Now imagine that the bubble is much smaller, by thousands of times, and that there are millions of them packed closely together. Not only would the resulting structure be very strong, but because it is mostly air, it would also be very good at keeping heat on one side and cool on the other. This is essentially what an aerogel is.
In the past the process of making aerogels has been quite difficult and expensive. This is due to the fact that the gel that supports the shell of each sphere must evaporate without destroying the very shell it supports. In other words, the supporting structure, the gel, must be removed without surface tension tearing the bubble shell apart. Since evaporation typically causes the surface tension effect that pulls the shells apart a method to cause the gel to "disappear" without traditional evaporation had to be found. In the past this has been done by replacing the gel with acetone and then the resulting void with carbon dioxide at high temperatures and pressures. This method kept the pressures inside and outside the shell the same.
Aerogels have been called "solid smoke," "frozen smoke," or "blue smoke" based on their appearance. This appearance is due to the lattice of solid material causing the light that hits it to bounce off in many different directions within successive layers of the lattice.
The first aerogel was created to satisfy a bet. The bet was between Samuel Stevens Kistler, professor of chemistry, and Charles Learned. The bet was "to see if they could replace the liquid inside of jelly in a jar without causing any shrinkage." Kistler won the bet.
For a time Kistler worked for Monsanto Corporation developing aerogels as fillers for paint, but Monsanto eventually abandoned the concept in 1970...probably due to cheaper fillers and the high cost of creating aerogels.
By this time Kistler had returned to teaching by taking a post at the University of Utah. Kistler died in 1975, just before a resurgence in interest in aerogels.
Types of Aerogel
Aerogels are primarily defined by the substance that makes up the matrix, not the gas between the latticework. Aerogels are therefore categorized by the material that makes up the framework.
Silica (glass) aerogels are the most common type, Because it is the most common it is also the most extensively studied. Silica aerogel is the world's lowest-density solid at 1 mg/cm3 (milligram per cubic centimeter).; The density of air is 1.2 mg/cm3 meaning that air is more dense than the lightest silica aerogel.
To get some idea of a milligram imagine a dollar bill, which weighs a gram, cut up into one thousand pieces. Each piece would weigh a milligram.
Silica is not only a good thermal insulator in aerogels, it also absorbs infrared radiation. Such insulation materials allow light to enter buildings, but trap heat for solar heating.
It is higlhy thermally insulating. It has very low thermal conductivity corresponding to R-values of 14 to 105 for 3.5 inch thick bat depending on the structure. This means that a half-inch thick bat of aerogel has about the same insulating properties of three inches of fiberglass insulation. By comparison, typical fiberglass or celulose wall insulation has an R-Value of 3 for 3.5 inch thickness. Silica aerogel has a melting point of 2,192°F (1,200 °C).
Silica aerogels currently hold fifteen records in the Guinness Book of World Records for material properties, including best insulator and lowest-density solid.
Have similar properties to silica aerogels except that they can be conductive and are very good at gathering and retaining light generated heat. Carbon aerogels are a primary material of study in supercapacitors.
Other aerogels have been created with alumina and agar (seaweed). These gels have slightly different properties than silica and carbon aerogels, but they all have high thermal insulation values. Agar aerogels are not only biodegradable, they are edible.
Properties of Aerogels
Aerogels have many properties not the least of which are the ability to limit thermal transfer.
Silicon Aerogels are:
- Thermal insulators
- Have sound absorption properties
- Desiccant (moisture absorption) properties
- Are Flameproof
- Are Water permeable (allows breath-ability)
Carbon Aerogel have all of the above properties plus:
- Are electrically conductive
- Can store electrical charge (as a capacitor medium)
- Absorb Infrared & visible light
Alumina Aerosols have all of the Silicon aerogel properties plus:
- Can act as a catalyst
SEAGel have all of the Silicon aerogel properties plus:
- Are biodegradable (edible)
Existing Uses of Aerogel
NASA has used aerogels in the Mars rovers to keep them from freezing in the sub-zero temperatures on the surface.
NASA has also used aerogels to trap dust streaming off of a comet in the "Stardust" collector experiment.
Dunlop is developing a tennis racket with aerogel filler. The idea is to create a racket that is very strong and extremely light in weight.
Insulating skylight material encased in Lexan is translucent. Because aerogel transmits scattered light there is not a suitable form of aerogel for windows...yet. Cabot makes the "nanogel" material for the skylights.
Laken makes a water-bottle insulated with aerogel.
Polarwrap makes shoe inserts made of sandwiched aerogel.
Aerogem makes jewelry made with aerogel.
Aspen Aerogeltm makes aerogel blankets that are capable of limiting heat pollution from operating equipment as well as quieting machinery covered in this blankets. These blankets are primarily industrial in use.
New Aerogels for Living
New aerogels are now being manufactured more cheaply and plentifully. One of the original drawbacks of an aerogel was it's fragility. Aerogels of the past, though very efficient at thermal insulation, were also very brittle making them poor candidates for building material.
Lately manufacturers have come up with ways of embedding aerogels in flexible plastic thereby creating sheets or bats of the substance.
In this way manufacturered insulating aerogels are similar to fiber reinforced plastic. Another benefit of these new materials is that they are opaque. They also retain low weight and much easier to work with. Unlike fiberglass bat, aerogel bat does not pose a breathing risk nor does it irritate the skin.
Aerogel bat is still more expensive than equivalent cellulose or fiberglass bat, but the prices are coming down. There are now three manufacturers of aerogel insulation; each listed below.
The author owns no stock nor has been compensated in any way for the contents of this article. None of the companies listed paid the author monetarily, with discounts, or freebies for this write-up.
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