Tech Briefs Magazine - April 2021 - 21

0.5
0.45
0.4

% TML

0.35
0.3
0.25
0.2
0.15
0.1
0.05
0
0

Time (h)
CV-1142
SCV1-2596
SCV-2585
SCV1-2590

CV-1144-0
CV-2680-12
SCV-2586

CV-1152
CV4-1161-5
CV10-2568

CV-2646
CV-2289-1
CV16-2500

Figure 3. Comparison of the TML % over time for silicones tested by ASTM E1559.

0.04

% TML

0.03

NuSil® space-grade silicones that were tested, along with their cure chemistry and
the application for each silicone tested.
In Figure 3, the silicone materials are
tested using ASTM E1559, evaluating
TML as a function of time. This testing
showed a sharp rise in TML during the
first two to four hours of the testing for
all samples. Then, the low-outgassing
materials started to level off between 24
to 48 hours, whereas the ultra-low-outgassing materials leveled off much earlier, within four to eight hours. When
comparing ultra-low-outgassing to lowoutgassing materials, TML is reduced by
approximately four to nine times.
The percentage of CVCM measured
by ASTM E1559 testing was just as
important as TML since the materials
that condensed were higher molecular
weight materials with lower volatility.
Figure 4 demonstrates the difference in
outgassing of volatiles over time when
comparing the low-outgassing and ultralow-outgassing materials. While all materials had CVCM of 0.04% over 72 hours
of testing, ultra-low-outgassing silicones
demonstrated their advantages by having CVCM values of 0.001%, a full
order of magnitude less compared to
the low-outgassing silicones.

Making the Right Choices
0.02

0.01

0
0

Time (h)
CV-1142
SCV1-2596
SCV-2585
SCV1-2590

CV-1152
CV4-1161-5
CV10-2568

CV-1144-0
CV-2680-12
SCV-2586

CV-2646
CV-2289-1
CV16-2500

Figure 4. Comparison of the VCM % (298 K QCM) over time for products tested by ASTM E1559.

for extended periods of time - even
decades - in space.
Recently, a silicone manufacturer analyzed a suite of its products, including
condensation and addition cure materials, using both ASTM E595 and E1559 to
detail and compare the purity and stability of the company's low-outgassing (CV
product designation) and ultra-low-outgassing product lines (SCV product designation) and their effects on outgassing
kinetics.

For the most stringent space applications, where even low amounts of volatiles might outgas from traditional
space-grade materials and cause potential problems, the manufacturer developed a suite of ultra-low-outgassing materials. These materials are held to a much
higher standard, with a TML of 0.1%
and CVCM 0.01% by ASTM E595.
In Figure 1, the percent of TML at the
end of testing is compared using ASTM
E595 versus ASTM E1559. Figure 2 lists the

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Cov

ToC

The testing demonstrates that ultralow-outgassing silicones offer an ideal
solution for sensitive areas where contamination must be kept to a minimum
to extend hardware operating life. The
testing also demonstrates the value of
working with a silicone supplier that is
able to provide advanced materials that
can stand up to the extreme environmental demands of space applications in
both low-outgassing and ultra-low-outgassing options.
A spacecraft's mission, its longevity,
and the sensitivity of the spacecraft's
instruments will help guide the selection
of a specific silicone, based on where it
will be used. When choosing a silicone,
it is important to remember the function, purity, and process requirements of
the application as well as the benefits of
working with silicone suppliers that have
extensive experience customizing spacegrade silicones to meet the needs of the
most advanced spacecraft.
This article was written by Dr. Timothy
Steckler, Applications Engineer, NuSil™ - a
brand of Avantor® -- Radnor, PA. For more
information, visit http://info.hotims.com/
79412-122.
21

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Tech Briefs Magazine - April 2021

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