scholarly journals High Temperature Microtribological Studies of MoS2 Lubrication for Low Earth Orbit

Lubricants ◽  
2020 ◽  
Vol 8 (4) ◽  
pp. 49 ◽  
Author(s):  
Peter Serles ◽  
Khaled Gaber ◽  
Simo Pajovic ◽  
Guillaume Colas ◽  
Tobin Filleter

Molybdenum disulfide is one of the most common lubricant coatings for space systems but it displays enormous susceptibility to environmental conditions making it hard to predict performance throughout the entire lifetime. The majority of mechanisms for space operate in low Earth orbit where temperatures typically reach 120 °C along with exposure to highly reactive atomic oxygen which can be detrimental to lubricant performance. In the present study, a MoS2 lubricant coating is tested using friction force microscopy under different environmental conditions including air and dry nitrogen environments with temperatures ranging from 25 °C to 120 °C. The increased temperature was found to be beneficial for friction behaviour in air up to 100 °C as ambient humidity is removed from the contact, but higher temperatures become detrimental as increased reactivity leads to oxidation. These competing effects resulted in a minimum coefficient of friction at 110 °C in the air environment. The high temperature also increases the wear of the coatings as the intrinsic shear strength decreases with thermal energy which in turn disrupts tribofilm formation leading to increased friction. The run-in duration and magnitude are both found to decrease with temperature as the energy barrier to optimal reconfiguration is reduced. Finally, contextualization of the present findings for mechanisms operating in low earth orbit is discussed.

2000 ◽  
Vol 12 (1) ◽  
pp. 43-52 ◽  
Author(s):  
John W Connell

Thin films of phenylphosphine oxide-containing polymers were exposed to low Earth orbit aboard a space shuttle flight (STS-85) as part of flight experiment designated Evaluation of Space Environment and Effects on Materials (ESEM). This flight experiment was a cooperative effort between the NASA Langley Research Center (LaRC) and the National Space Development Agency of Japan (NASDA). The thin-film samples described herein were part of an atomic oxygen exposure (AOE) experiment and were exposed to primarily atomic oxygen (∼1×1019 atoms cm−2). The thin-film samples consisted of three phosphine oxide-containing polymers (arylene ether, benzimidazole and imide). Based on post-flight analyses using atomic force microscopy, x-ray photo-electron spectroscopy and weight loss data, it was found that the exposure of these materials to atomic oxygen (AO) produces a phosphorus oxide layer on the surface of the samples. Earlier work has shown that this layer provides a barrier towards further attack by AO. Consequently, these materials do not exhibit linear erosion rates which is in contrast with most organic polymers. Qualitatively, the results obtained from these analyses compare favourably with those obtained from samples exposed to AO and/or an oxygen plasma in ground-based exposure experiments. The results of the low Earth orbit AO exposure on these materials will be compared with those of ground-based exposure to AO.


1998 ◽  
Author(s):  
J. A. Schultz ◽  
K. Eipers-Smith ◽  
K. Waters ◽  
S. Schultz ◽  
M. Sterling ◽  
...  

1991 ◽  
Vol 236 ◽  
Author(s):  
Jeffrey S. Hale ◽  
R.A. Synowicki ◽  
S. Nafis ◽  
John A. Woollam

AbstractCVD deposited diamond-like carbon (DLC) films have been studied for possible use as a secondary standard for Low Earth Orbit materials degradation. Samples of various thicknesses have been exposed to a simulated Low Earth Orbit atomic oxygen (AO) environment using a plasma asher. Mass loss measurements indicate that DLC degrades at a rate of 0.7 mg/hr which is two to three times the rate of currently used Kapton samples which degrade at a rate of.3 mg/hr. Thickness measurements show that DLC thins at a rate of 77 Angstroms/min. Since DLC is not as susceptible to environmental factors such as moisture absorption, it could potentially provide more accurate measurements of AO fluence on short space flights. Adhesion of DLC films to both fused silica and crystalline silicon substrates has been studied under thermal cycling conditions. Film adhesion to fused silica can be enhanced by sputtering a thin layer of silicon dioxide onto the substrate prior to deposition. In addition to the above, the index of refraction and extinction coefficient of various thicknesses of DLC films has been characterized by Variable Angle Spectroscopic Ellipsometry.


2021 ◽  
pp. 1-10
Author(s):  
Carlos A. Maldonado ◽  
Andrew D. Ketsdever ◽  
John D. Williams

1992 ◽  
Author(s):  
BRUCE BANKS ◽  
SHARON RUTLEDGE ◽  
LINDA GEBAUER ◽  
CINDY LAMOREAUX

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