Elastomerics Blog

Low outgassing, conductive silicones are specialized elastomers that combine shielding against electromagnetic interference (EMI) with low levels of outgassing: the release of trapped, dissolved, or absorbed gases from solid materials when exposed to heat or vacuum conditions. Because these elastomers are silicone-based, they also provide environmental sealing and thermal insulation.

Stockwell Elastomerics sources low outgassing, conductive silicones from supplier partners and cuts or molds these solid materials into seals, gaskets, and grounding pads. Applications include satellites and spacecraft, optical instruments and imaging payloads, defense avionics, and cleanroom electronics. Space is an important application, but there are terrestrial uses as well.

What are Low Outgassing, Conductive Silicones?

Low outgassing, conductive silicones meet ASTM E595 and/or NASA standards for the release of gases or volatiles compounds from a material that’s exposed to a vacuum or heat. ASTM E595 defines the framework for measuring specific values and is used by industry. NASA’s own standards refer to ASTM E595 and define acceptable limits for spacecraft and space vehicles.

In space environments, low outgassing silicones will not release substances that could cloud optics, electronics or sensors under near-vacuum conditions. When they are electrically conductive, they contain particles that allow electricity to flow from one conductive surface to another. Particle types include nickel-aluminum, silver- aluminum, and nickel-graphite.

Some low outgassing, conductive silicones meet standards such as MIL-DTL-83528 Type B or D for EMI gaskets, a consideration for military applications. There are also materials that combine low outgassing and EMI shielding with a UL 94V-0 flame rating, or that can meet ASTM D1329 requirements for evaluating rubber retraction at low temperatures.

For some applications, EMI materials that are not formulated to be low outgassing may undergo a post-cure process in order to make them capable of meeting ASTM outgassing standards. Stockwell can advise on which materials may be eligible for post-cure.

Understanding the Benefits and Applications

In vacuum or high-temperature environments, standard silicones can release vapors that fog lenses, degrade detectors, or interfere with thermal control surfaces.  Low outgassing, conductive silicones reduce these risks while providing the electrical conductivity, EMI shielding, environmental sealing, and thermal insulation that some applications also require.

As silicone-based products, these materials can withstand a wider range of temperatures and more extreme temperatures than compounds based on elastomers like EPDM. Low outgassing, conductive silicones also resist thermal cycling, the repeated heating and cooling of a material or device between two temperature extremes.

That’s important because while space is very cold, the surfaces of satellites heat up as they absorb solar radiation. For example, surfaces facing the sun in Earth’s orbit can reach around 250°F (120°C) while those in shadow can fall to -250°F (-150°C). Silicones can withstand lower temperatures than some other elastomers, but specialized silicones are needed for the extreme cold of outer space.

Low outgassing, conductive silicones aren’t just for space, however. In cleanroom electronics, they’re used with shielded enclosures for metrology tools, sensor housings, high-frequency test equipment, cleanroom robotics, and medical imaging electronics. Materials with a fluorosilicone base are available for applications that must resist the aggressive chemicals found in some cleaners.

Find Low Outgassing, Conductive Silicones

Low outgassing and conductivity are challenging demands that offer numerous benefits in application. Stockwell Elastomerics can help you with material selection to meet both of these requirements. To talk to our Applications Engineering Team, complete our on-line form, email service@stockwell.com, or call (215) 335-3005.