5 Things to Know Before Buying Silica Aerogel Insulation

Synthetically producing amorphous silica gel and then infusing it into a fabric creates what many buyers know as aerogel insulation according to one distributor&#;s website. Amorphous silica appears on state hazardous substance lists for California and New Jersey. According to the website TeachEngineering,org, Samuel Stephens Kistler invented aerogel in . Not unlike Kistler&#;s approach to inventing aerogel, some manufacturers today create aerogels by putting together a polymer and solvent, which forms a gel; they then remove the liquid and replace it with air. In some cases, manufacturers use silica, or silicon dioxide, with a solvent to make the gel, extract the fluid and insert carbon dioxide. Some aerogel manufacturers include titanium dioxide TiO2 as an ingredient, which the International Agency for Research on Cancer (IARC) classifies as a Group 2B carcinogen, possibly carcinogenic if inhaled.  A article from the Archives of Toxicology, titled &#;Health hazards due to the inhalation of amorphous silica,&#; notes &#;Inflammatory responses and emphysema have been described in a number of animal studies, especially in rats and monkeys.&#;

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Some manufacturers of aerogels advocate for their use because they prevent heat transfer and are lightweight. For example, according to ExtremeTech, graphene aerogel is remarkably light, weighing about 160 grams per cubic meter.

According to InspectAPedia.com, the R-Value of aerogel is 10.3 per inch versus rigid fiberglass, which has an R-Value of 4 per inch. The R-Value, or resistance value, of insulation measures to what degree insulation resists the flow of heat through an insulation material. As the R-Value climbs from 0 it signifies that the insulation material is doing a better job of preventing heat transfer, and consequently it&#;s a more effective barrier.

AEROGEL AS INSULATION

PROS

CONS

Lightweight Potential upper respiratory effects from inhaling and/or handling R-Value of 10.3/inch Use of PPE required
when handling K-Factor of .01 Amorphous silica listed as a hazardous substance[1] Per IARC, aerogel with TiO2 is possibly carcinogenic to humans if inhaled Emphysema due to inhalation described in animal studies

 

Some aerogel insulation makers also note the material has a low K-Factor, otherwise known as thermal conductivity. K-Factor is the rate at which heat flows through insulation material. Thermal conductivity as defined by ASTM Standard C168 is &#;the time rate of steady state heat flow through a unit area of a homogeneous material induced by a unit temperature gradient in a direction perpendicular to that unit area.&#; To simplify that, K-Factor is measuring the Btus of heat flowing through an inch-thick insulation material each hour across an area one foot by one foot for every degree of Fahrenheit change. Fiberglass has a K-Factor ranging from .22 to .30. By comparison, aerogels can have a K-Factor as low as .01.

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Along with aerogel&#;s publicized benefits, there was a report in March by the U.S. Department of Health and Human Services in response to concerns from an insulators&#; union about exposure to aerogel from handling the material. According to the insulators, they received aerogel insulation on rolls and then moved it to cutting rooms where students practiced measuring, cutting, and wrapping it. The department&#;s investigators visited the employer&#;s location in Illinois to analyze airborne exposure and air samples at a training facility where workers were being taught to work with aerogel insulation. What the HHS says it found was &#;Airborne exposures for amorphous silica approached calculated occupational exposure limits. Most aerogel particles were respirable in size. Many interviewed participants attributed respiratory irritation and very dry skin to handling aerogel insulation. We recommended continued use of personal protective equipment per manufacturer&#;s safety data sheets to minimize reported health effects.&#; That said, due to the limited scope of this analysis (i.e., one sample from one instructor providing aerogel instruction), the HHS report states its &#;results may not be generalizable to other workplace settings.&#; However, the report also states that employers should &#;educate staff and students about potential upper respiratory tract irritation and drying effects from prolonged exposure to aerogel insulation.&#;

[1] Right to Know Hazardous Substance List, New Jersey Department of Health and Senior Services, CAS -00-8

Aerogels are extremely good thermal insulators for several reasons. First, it is important to understand how heat is transported through materials. Heat is transported through a material three different ways: through conductive transport, that is, through the solid part of the material; through convective transport, that is, by being carried by gas diffusing through a material; and through radiative transport, that is, by electromagnetic energy like infrared energy penetrating through the material.

Aerogels are extremely low-density materials, typically 50-99.98% air by volume. This means aerogels have very little mass through which heat can conduct. Additionally, the solid part of an aerogel is highly disordered and thus makes conduction of heat through the little solid that is there inefficient.

Additionally, aerogels have extremely tiny pores, typically between 2-50 nm in diameter. These pores are actually so tiny that they are smaller than the mean free path of air at room temperature and pressure, that is, the average distance a molecule of air can travel before hitting another air molecule is greater than the width of the pores in a typical aerogel. As a result, air has an extremely difficult time diffusing through and thus carrying heat energy through an aerogel by convection. This phenomenon, called the Knudsen effect, differentiates aerogels from traditional foams, which typically have pore sizes of tens to thousands of microns in diameter and thus allow more heat through by convection.

Aerogels are not necessarily good at stifling radiative transport, however, and so at high temperatures, heat can pass through aerogels in the form of infrared energy. As a result, commercial aerogel insulation products include additional materials called IR opacifiers embedded in the aerogel to reflect and/or absorb infrared energy. This helps limit radiative transport, making aerogel insulators excellent insulators at high temperatures as well as room temperature.

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