Henry C. de Groh III, Bernadette J. Puleo, and Bruce M. Steinetz

Glenn Research Center, Cleveland, Ohio

Effects of Atomic Oxygen and Grease on

Outgassing and Adhesion of Silicone Elastomers

for Space Applications

NASA/TM—2012-217263

February 2012
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Henry C. de Groh III, Bernadette J. Puleo, and Bruce M. Steinetz

Glenn Research Center, Cleveland, Ohio

Effects of Atomic Oxygen and Grease on

Outgassing and Adhesion of Silicone Elastomers

for Space Applications

NASA/TM—2012-217263

February 2012

National Aeronautics and

Space Administration

Glenn Research Center

Cleveland, Ohio 44135

Prepared for the

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Space Environment (ICPMSE-10J)

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and the Society for Promotion of Space Science

Bankoku-Shinryokan, Okinawa, Japan, June 12–17, 2011
Acknowledgments

The authors wish to thank Bruce Banks and Sharon Miller for their assistance with atomic-oxygen (AO) exposures,

Mark Jaster for his help with heat treatments, and William Anderer for mechanical support.

Available from

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subject to revision as analysis proceeds.
NASA/TM—2012-217263 1 

Effects of Atomic Oxygen and Grease on Outgassing and 

Adhesion of Silicone Elastomers for Space Applications 

Henry C. de Groh III, Bernadette J. Puleo, and Bruce M. Steinetz 

National Aeronautics and Space Administration 

Glenn Research Center 

Cleveland, Ohio 44135 

Abstract 

An investigation of silicone elastomers for seals used in docking and habitat systems for future space 

exploration vehicles is being conducted at NASA. For certain missions, NASA is considering 

androgynous docking systems where two vehicles each having a seal would be required to: dock for a 

period of time, seal effectively, and then separate with minimum push-off forces for undocking. Silicone 

materials are generally chosen for their wide operating temperatures and low leakage rates. However 

silicone materials are often sticky and usually exhibit considerable adhesion when mated against metals 

and silicone surfaces. This paper investigates the adhesion unit pressure for a space rated silicone material 

(S0383-70) for either seal-on-seal (SoS) or seal-on-aluminum (SoAl) operation modes in the following 

conditions: as-received, after ground-based atomic-oxygen (AO) pre-treatment, after application of a thin 

coating of a space-qualified grease (Braycote 601EF), and after a combination of AO pre-treatment and 

grease coating. In order of descending adhesion reduction, the AO treatment reduced seal adhesion the 

most, followed by the AO plus grease pre-treatment, followed by the grease treatment. The effects of 

various treatments on silicone (S0383-70 and ELA-SA-401) outgassing properties were also investigated. 

The leading adhesion AO pre-treatment reduction led to a slight decrease in outgassing for the S0383-70 

material and virtually no change in ELA-SA-401 outgassing. 

1.0 Introduction 

The National Aeronautics and Space Administration (NASA) is evaluating different silicone 

elastomers for seals for docking and habitat systems being considered for future missions (Refs. 1 and 2). 

In addition to exhibiting extremely low leakage, the seals must meet stringent low-outgassing 

requirements, operate over a broad temperature range, and exhibit low adhesion to minimize decoupling 

or separation forces. The primary class of elastomers that meet the wide operating temperature range for 

these applications are silicone-based rubbers (Ref. 3). However, these elastomers have inherent adhesive 

properties, which make them sticky, creating potential difficulties when trying to separate docked 

spacecraft or hatches (Refs. 4 and 5). Three different adhesion-lowering treatments have been considered: 

atomic oxygen (AO), grease coating, and an AO treatment combined with a grease coating. A heat 

treatment plus AO treatment was examined in an effort to lower outgassing. The AO pre-treatment 

developed by NASA Glenn has shown excellent results in reducing seal adhesion with moderate fluence 

levels (Refs. 4 and 6). Grease was considered in two approaches: first as a stand-alone treatment and 

second as an addition to the baseline AO pre-treatment method. Grease was investigated as a means to 

reduce adhesion for the following reasons: its effectiveness at lowering adhesion was unknown; the AO 

pre-treatment, though very effective, requires special equipment and a vacuum tank large enough to 

accommodate the seal diameter; and the special equipment costs make AO treatments expensive 

compared to grease. The effects of a light grease coating on adhesion and outgassing are presented here. 

Several different elastomer compounds have been considered and tested; this paper is limited to results 

from tests of the elastomer compounds S0383-70 supplied by Parker-Hannifin Corporation, and ELA-SA401 supplied by Esterline Corporation. 

 
NASA/TM—2012-217263 2 

Prior work has shown that atomic oxygen, characteristic of that present in Low-Earth-Orbit (LEO) 

combines with the silicone in silicone-based elastomers to form a very thin, glassy surface coating 

(Refs. 4 and 7). At moderate AO levels, this SiOx-based coating does not significantly degrade the sealing 

properties of the rubber (Ref. 6). 

Space-qualified grease has been used in the past by NASA to lubricate gears and to ease the 

placement of elastomer seals (Refs. 8 and 9). Greases are also being considered as a way to lower 

unwanted seal adhesion. Braycote Micronic 601 EF, a space qualified perfluoroether grease, was 

examined in this study (Ref. 10). 

When elastomer seals are used in space, it is important for them to be stable, and have a low total 

mass loss (TML) and low collected volatile condensable materials (CVCM). Current requirements are for 

TML 1 percent and CVCM 0.1 percent. However, there is always motivation for outgassing to be as 

low as possible to minimize contamination of sensitive surfaces such as windows and tracking systems. 

Thus tougher requirements are frequently proposed and may be imposed in some situations in the future. 

The effects of AO and grease coatings on seal outgassing were unknown, thus a campaign was begun 

to determine the effects of these treatments on TML and CVCM. This paper reports the results of that 

campaign. 

2.0 Procedures 

2.1 Specimens 

This study used cylindrical button specimens cut from sheets to measure adhesion, and #2-106 

o-rings to measure outgassing. 

2.1.1 Buttons for Adhesion Testing 

Cylindrical 9.1 mm diameter buttons of S0383-70 elastomer were cut from 5.4 mm thick sheet 

material using a drill press and a custom-made core drill lubricated with soap, as described previously 

(Ref. 6). Buttons to be tested with grease were then weighed, and an amount of Braycote Micronic 601 

EF grease approximating 1.2 mg/cm2

 applied to its mating surface. Small amounts of grease were then 

added or subtracted to achieve the desired rate of 1.2 mg/cm2

. The adhesion buttons had an average rate 

of coverage of 1.17 mg/cm2

 and a standard deviation of 0.11 mg/cm2. Only S0383-70 buttons were made; 

no adhesion tests on ELA-SA-401 are reported in this paper. 

2.1.2 O-rings for Outgas Testing 

This study used S0383-70 and ELA-SA-401 o-rings of the size #2-106 (inner diameter = 4.42 mm 

and cord width = 2.62 mm) which were small enough to fit in the crucible used in outgas testing without 

being cut or sectioned in any way. It was believed that sectioning after AO treatment, and there-by 

exposing the sample’s interior, could increase outgassing (Ref. 6). Sheet material was not used because 

the process by which the o-rings are made mimics better the docking seal manufacturing process. 

2.2 Treatments 

2.2.1 Atomic Oxygen 

Elastomer S0383-70 button specimens to be tested with grease were AO exposed in an atomic oxygen 

facility, referred to as Tank 9 at the NASA Glenn Research Center (GRC) (Ref. 6), to a fluence of 

1.251020 atoms/cm2

. Fluence levels in the facility were determined using Kapton witness specimens. 

O-rings for grease and outgas testing made of S0383-70 and ELA-SA-401 were AO exposed to 

1.01020 atoms/cm2

 using SPI Supplies Plasma Prep II atomic oxygen facilities at GRC (Ref. 6). O-rings 

were hung by a fine wire to insure AO exposure to all surfaces. Another set of o-rings were exposed to a 

fluence of 4.91020 atoms/cm2

 after a 4- day vacuum bake in a related effort to lower outgassing. 
NASA/TM—2012-217263 3 

2.2.2 Heat Treatments 

In an effort to lower TML and CVCM a treatment was used on S0383-70 and ELA-SA-401 

o-rings which consisted of a 4-day bake under vacuum at a temperature of 205 C, after which, the 

o-rings were exposed to an AO fluence of 4.91020 atoms/cm2

. 

2.2.3 Grease Coating 

As-received buttons and #2-106 o-rings to be greased were first wiped with 99 percent isopropyl 

alcohol, dried, and weighed. The procedure used to grease the buttons is mentioned in Section 2.1.1. The 

o-rings were covered with Braycote Micronic 601 EF perfluoroether grease over their entire surface at an 

average rate of 1.19 mg/cm2

 with a standard deviation among o-rings of 0.08 mg/cm2. The rate of 

coverage was measured by weighing the o-ring before and after grease application and the amount of 

grease adjusted until the desired coverage was achieved. To put this application rate into perspective the 

Sun Protection Factor (SPF) application rate for sunscreen on a person’s skin is 2 mg/cm2

. 

2.3 Adhesion Testing 

Procedures used for adhesion testing are discussed in detail elsewhere (Ref. 6). Adhesion was 

measured between the flat surfaces of two buttons SoS and between a button and a flat, anodized 

aluminum alloy plate SoAl with the plate having an average roughness, Ra, of 13 in. (0.33 μm). The 

aluminum alloy was 6061 T651 and the anodizing was MIL-A-8625 T II. Button specimens were brought 

together, compressed 25 percent, and held for 72,000 sec (20 hr). The load and unload rate was 0.01 in./s 

(0.254 mm/s). Adhesion was measured during unloading using a force transducer. Specimens mated with 

other specimens with a similar grease coating were tested repeatedly. Once a grease coated button was 

mated with an uncoated specimen, such as an anodized aluminum plate, the greased button would not be 

tested again until its coating had been re-applied and measured. The anodized aluminum plate used in 

SoAl tests was cleaned with 99 percent isopropyl alcohol before each test. 

2.4 Outgas Testing 

All o-ring outgas test specimens were sent to Orange County Material Test Laboratories in Anaheim, 

California, who used ASTM Standard Designation: E 595-93 (Ref. 11) for TML and CVCM testing. 

3.0 Results 

3.1 Adhesion 

Figure 1 shows the adhesion of the compound S0383-70 in the various sealing modes of interest, sealon-seal SoS and seal-on-aluminum SoAl and with various treatments imposed on the rubber. This group of 

experiments was designed to determine if Braycote Micronic 601 EF perfluoroether grease could be used to 

lower the adhesive characteristics of S0383-70. The bar data in Figure 1 are the averages listed in Table 1. 

The lines in the bars of data represent the range of values from the tests performed and can also be found in 

Table 1. Figure 1 shows the as-received adhesion and how effective an AO treatment of 1.251020 atoms/ 

cm2

 is, effectively lowering SoS and SoAl adhesion to 0.5 psi or essentially zero. The application of 

1.2 mg/cm2

 of grease to as-received S0383-70 also lowered adhesion in both SoS and SoAl arrangements. 

Application of the grease resulted in an approximately 70 percent decrease in adhesion compared to asreceived levels. This level of adhesion reduction achieved with grease only may be of value in many 

applications. However, the goal for future docking systems is for the seal adhesion to be below 0.5 psi. The 

adhesion of AO treated S0383-70 increased with the application of the grease to about 5 psi for the SoS 

case, and 3 psi for SoAl. These conservative (worst case) values of 5 and 3 psi for the AO + grease tests are 

cited rather than the averages of 2.74 and 1.1 psi for SoS and SoAl, respectively because of the stochastic 

nature of adhesion and adhesion testing which is reflected by the standard deviations provided in Table 1. 
NASA/TM—2012-217263 4 

Figure 1.—Adhesion in lb/in.2 of S0383-70 elastomer in Seal-on-Seal (SoS) and Sealon-aluminum (SoAl) test modes, in the following conditions: 1. As-received; 2. After 

receiving an atomic oxygen fluence of 1.251020 atoms/cm2

 AO; 3. After application 

of Braycote Micronic 601 perfluoroether grease at a rate of 1.2 mg/cm2

; 4. 

After1.251020 atoms/cm2

 AO plus 1.2 mg/cm2 Braycote Micronic 601 grease. 

TABLE 1.—ADHESION IN lb/in.2 of S0383-70 ELASTOMER IN SEAL-ON-SEAL AND SEAL-ON-ALUMINUM TEST 

MODES CONDITIONS: AS RECEIVED, AO FLUENCE OF 1.251020 ATOMS/cm2

, APPLICATION OF BRAYCOTE 

MICRONIC 601 EF PERFLUOROETHER GREASE, AND A COMBINATION OF AO FLUENCE OF 

1.251020 ATOMS/cm2

 PLUS BRAYCOTE MICRONIC 601 EF PERFLUOROETHER GREASE 

 As-received w/AO w/Grease w/AO+Grease 

Test # SoS SoAl SoS SoAl SoS SoAl SoS SoAl 

1 24.67 4.28 0.37 0.34 3.75 1.83 0.16 0.37 

2 20.1 10.73 0.02 0.02 10.83 1.85 5.23 0.18 

3 35.51 3.1 -------- -------- 11.66 0.91 5.33 3.51 

4 -------- -------- -------- -------- -------- -------- 0.23 0.32 

Average 26.76 6.04 0.20 0.18 8.75 1.53 2.74 1.10 

Standard 

deviation 

6.46 3.35 0.18 0.16 3.55 0.44 2.54 1.40 

3.2 Outgassing 

Outgas testing of as-received material and after the 4-day vacuum bake + AO, AO only treatment, 

and grease coating, are shown in Figure 2. All outgassing data are from uncut, #2-106 o-rings. Per the 

ASTM standard each measurement was an average of 3 o-ring tests; one repeat measurement was made 

for the tests using grease and the two measurements then averaged. 

The combined bake at 205 C and AO treatment did not lower the outgassing of S0383-70 

significantly compared to as-received S0383-70, however the combined bake at 205 C plus AO 

treatments did lower TML by 78 percent and CVCM by 69 percent for ELA-SA-401. Thus ELA-SA-401 

may be advantageous in applications where very low outgassing is needed. 

Figure 2 represents the effects of the 1.251020 atoms/cm2

 AO fluence on outgassing of both the 

S0383-70 and ELA-SA-401 compounds. A slight decline in outgas is observed for the S0383-70 

compound relative to as-received. ELA-SA-401 did not show a significant change in outgas properties 

after the AO treatment. 
NASA/TM—2012-217263 5 

Figure 2.—Effect of heat treatment + Atomic Oxygen (AO), Atomic Oxygen, and grease 

coating on the outgassing of S0383-70 and ELA-SA-401. 

Figure 2 shows a slight increase in outgassing for S0383-70, compared to as-received, after the 

application of 1.2 mg/cm2

 of Braycote Micronic 601 EF perfluoroether grease. However the greased seal 

still achieves NASA’s outgas requirements of TML 1 percent and CVCM 0.1 percent. Based on the 

standard deviation of TML and CVCM measurements and expected detection limits, the uncertainty of 

TML and CVCM results is judged to be 0.02 percent: this uncertainty is shown as error bars on Figure 2 

(Ref. 12). 

4.0 Conclusions 

A number of adhesion tests were conducted on silicone elastomer Parker S0383-70 material. Of the 

various adhesion reduction techniques evaluated, the AO pre-treatment of 1.251020 atoms/cm2

 lowered 

adhesion the most. For seal-on-seal (SoS) operation modes the seals showed reduced unit adhesion from 

26.8 to 0.2 psi and for seal-on-aluminum (SoAl) operation modes unit adhesion went from 6.04 to 

0.18 psi. Application of a thin coat of Braycote 601EF perfluoroether grease also reduced adhesion, but to 

a lesser degree; for SoS the unit adhesion went from 26.8 to 8.75 psi and for SoAl the unit adhesion went 

from 6.04 to 1.53 psi. For specimens that were first pre-treated with AO and further applied with a thin 

coat of Braycote Micronic 601EF perfluoroether grease the reduction in unit adhesion for SoS went from 

26.8 to 2.74 psi and SoAl went from 6.0 to 1.10 psi. The AO pre-treatment enables S0383-70 to achieve 

the low adhesion levels we expect to need for docking seal applications (2 psi). 

Outgassing in ELA-SA-401 was not changed after AO pre-treatment of 1.251020 atoms/cm2

. 

However, after the bake plus AO pre-treatment the TML and CVCM of ELA-SA-401 decreased by 

78 and 69 percent, respectively. Outgassing in S0383-70 slightly decreased after AO pre-treatment and 

did not significantly change after the bake plus AO treatment. Outgassing was higher for Braycote 601EF 

perfluoroether grease-coated S0383-70 compared to as-received S0383-70, however the outgassing with 

applied grease was still below NASA’s TML and CVCM percentage requirements of TML 1 percent 

and CVCM 0.1 percent. 
NASA/TM—2012-217263 6 

References 

1. “Overview of LIDS Docking Seals Development,” Pat Dunlap, B. Steinetz, and C. Daniels, 2008 

NASA Seal/Secondary Air System Research Symp., NASA/CP—2009-215677. 

2. Lewis, J.L., Carroll, M.B., Morales, R.H., and Le, T.D., National Aeronautics and Space 

Administration (U.S. Government), Washington, D.C., “Androgynous, Reconfigurable Closed 

Loop Feedback Controlled Low Impact Docking System with Load Sensing Electromagnetic 

Capture Ring,” U.S. Patent No. 6,354,540, March 12, 2002. 

3. “Apollo Seals: A Basis for the Crew Exploration Vehicle Seals,” J.R. Finkbeiner, P.H. Dunlap Jr., 

B.M. Steinetz, C.C. Daniels, AIAA–2006–5259, presented at the 42nd AIAA/ASME/SAE/ASEE 

Joint Propulsion Conf. Sacramento CA, 2006; also available as NASA/TM—2006-214372. 

4. “Adhesion of Silicone Elastomer Seals for NASA’s Crew Exploration Vehicle,” H.C. de Groh III, 

S.K.R. Miller, I.M. Smith, C.C. Daniels, and B.M. Steinetz, 44th AIAA/ASME/SAE/ASEE, Joint 

Propulsion Conference, July 2008, Paper No. AIAA-2008-4625, July 21, 2008 Hartford, CT; also 

printed as NASA/TM—2008-215433. 

5. “An Experimental Investigation of Silicone-to-Metal Bond Strength in Composite Space Docking 

System Seals,” M.C. Conrad, C.C. Daniels, and M.B. Bastrzyk, NASA/CR—2010-216886, Oct. 

2010. 

6. “Space Environment Effects on Silicone Seal Materials,” H.C. de Groh III, Christopher C. 

Daniels, J.A. Dever, S.K. Miller, D.L. Waters, J.R. Finkbeiner, P.H. Dunlap Jr., and B.M. 

Steinetz, April 2010, NASA/TM—2010-216332. 

7. “Atomic Oxygen Interactions with FEP Teflon and Silicones on LDEF,” B.A. Banks, J.A. 

Dever, L. Gebauer, C.M. Hill, LDEF-69 Months in Space, page 801, Proceedings, NASA First 

Post-Retrieval Symp., 1991. 

8. “Performance and Analysis of Perfluorinated Grease Used on Space Shuttle Actuators,” W. 

Morales, K.W. Street Jr., and E.V. Zaretsky, April 2009, NASA/TM—2009-215605. 

9. “Process Specification for the Application of Liquid Lubricants,” Jay E. Bennett, Engineering 

Directorate, Structural Engineering Div., NASA JSC, Jan. 2007, PRC-8002C. 

10. “Product Data, Castrol Braycote Micronic 601 EF,” Castrol Industrial North America Inc., 

Naperville IL. 

11. ASTM Designation: E 595-93 (Reapproved 2003) ASTM International, 100 Barr Harbor Dr. PO 

Box C700, W. Conshohocken, PA 19428-2959, USA. Test Report for: Mass Loss and Collected 

Volatile Condensable Materials, NuSil Silicone Technology LLC, Carpinteria CA, 2006. 

12. Test Report for: Mass Loss and Collected Volatile Condensable Materials, NuSil Silicone 

Technology LLC, Carpinteria CA, 2006. 
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Effects of Atomic Oxygen and Grease on Outgassing and Adhesion of Silicone Elastomers 

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14. ABSTRACT

An investigation of silicone elastomers for seals used in docking and habitat systems for future space exploration vehicles is being 

conducted at NASA. For certain missions, NASA is considering androgynous docking systems where two vehicles each having a seal would 

be required to: dock for a period of time, seal effectively, and then separate with minimum push-off forces for undocking. Silicone materials 

are generally chosen for their wide operating temperatures and low leakage rates. However silicone materials are often sticky and usually 

exhibit considerable adhesion when mated against metals and silicone surfaces. This paper investigates the adhesion unit pressure for a 

space rated silicone material (S0383-70) for either seal-on-seal (SoS) or seal-on-aluminum (SoAl) operation modes in the following 

conditions: as-received, after ground-based atomic-oxygen (AO) pre-treatment, after application of a thin coating of a space-qualified grease 

(Braycote 601EF), and after a combination of AO pre-treatment and grease coating. In order of descending adhesion reduction, the AO 

treatment reduced seal adhesion the most, followed by the AO plus grease pre-treatment, followed by the grease treatment. The effects of 

various treatments on silicone (S0383-70 and ELA-SA-401) outgassing properties were also investigated. The leading adhesion AO pretreatment reduction led to a slight decrease in outgassing for the S0383-70 material and virtually no change in ELA-SA-401 outgassing.

15. SUBJECT TERMS

Elastomers; Grease; Coating; O-ring seals; Docking; Adhesion; Heat treatment; Rubber; Leakage; Silicones 

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