Paper TR+SE-WeM12
Synthesis and Tribology of MoS₃ Nanoparticles

Wednesday, October 31, 2012, 11:40 am, Room 19

There has been recent interest in the use of solid lubricant nanoparticles in coatings and as boundary additives in liquid lubricants. Examples include nanoparticles of MoS₂ and WS₂. The formation of these nanoparticles is nontrivial, requiring techniques such as gas phase syntheses and electric discharges. We are exploring simpler syntheses using wet chemical techniques. In particular, the synthesis of MoS₃ nanoparticles involves hydrothermal reaction between molybdate salts and sodium sulfide under controlled pH conditions.¹

The use of MoS₃ as a tribological material has not been explored beyond its use as an oil additive.² We are investigating its potential for use in solid lubricant coatings. Bonded MoS₂ coatings experience widespread usage for lubricating mechanisms on virtually every spacecraft (i.e., using micron-sized MoS₂ particles). We formulated resin-bonded coatings using MoS₃ nanoparticles as the lubricating pigment, and compared their tribological performance to commercial bonded MoS₂ coatings. Surprisingly, the MoS₃-formulated coatings performed similarly to the MoS₂-based coatings. Specifically, they showed similar coefficients of friction (i.e., 0.04 to 0.06) and endurances in dry nitrogen (<0.1% RH). We will present results of surface analyses on worn coatings to reveal changes in composition and chemical state of the MoS₃ that might explain the measured low friction. In addition, results of tribological performance in humid air atmospheres will be presented.

We have also explored syntheses of MoS₂ nanoparticles using nanosize MoS₃ as a starting material. A recent study purported to create MoS₂ nanoparticles with the addition of an aqueous reducing agent during hydrothermal synthesis of MoS₃.³ However, X-ray fluorescence analysis of the product of our synthesis showed that the S:Mo remained at 3.0 after using the reducing agent. Other conversion methods including vacuum reduction of the MoS₃ nanoparticles will be discussed.

References:

1. P. Afanasiev, “Synthetic approaches to the molybdenum sulfide materials,” Comptes Rendus Chimie, 11(1–2) (2008) 159–182.

2. O.P. Parenago, V.N. Bakunin, G.N. Kuz’mina, A.Yu. Suslov, and L.M. Vedeneeva, “Molybdenum Sulfide Nanoparticles as New-Type Additives to Hydrocarbon Lubricants,” Doklady Chemistry, 383(1-3) (2002) 86-88.

3. Y. Tian, X. Zhao, L. Shen, F. Meng, L. Tang, Y. Deng, Synthesis of amorphous MoS₂ nanospheres by hydrothermal reaction,” Materials Letters 60 (2006) 527–529.

This work was funded in part by The Aerospace Corporation's Sustained Experimentation and Research for Program Applications program.

© The Aerospace Corporation 2012