Abstract
Layered palygorskite (PAL), commonly called attapulgite, is a natural inorganic clay mineral composed of magnesium silicate. In this study, an aqueous miscible organic solvent treatment method is adopted to prepare molybdenum-dotted palygorskite (Amo-PMo) nanoplatelets, which greatly improved the specific surface area of PAL and the dispersion effect in an oil-based lubricant system. Their layered structure and size were confirmed using transmission electron microscopy (TEM) and atomic force microscopy. Following a tribological test lubricated with three additives (PAL, organic molybdenum (SN-Mo), and Amo-PMo), it was found that the sample of 0.5 wt% Amo-PMo exhibited the best tribological properties with a coefficient of friction of 0.09. Moreover, the resulting wear scar diameter and wear volume of the sliding ball surface were 63% and 49.6% of those lubricated with base oil, respectively. Its excellent lubricating performance and self-repairing ability were mainly attributed to the generated MoS2 adsorbed on the contact surfaces during the tribochemical reaction, thereby effectively preventing the direct collision between asperities on sliding solid surfaces. Thus, as-prepared Amo-PMo nanoplatelets show great potential as oil-based lubricant additives, and this study enriches the existing application of PAL in industry.
Highlights
Industries have been constantly seeking environmentally friendly and economical lubricants in an attempt to reduce energy waste caused by friction
The diffraction peaks observed for the Amo-PMo sample were at 2θ = 23.3°, 27.3°, and 39.1°, which were caused by MoO3, indicating that the synthesized material contained molybdenum
Compared with the Amo-PMo, the ball tested with PAL additives showed wider furrows on the sliding surfaces, and no Mg element distribution was present in the tribofilm, indicating that PAL could not be transferred to the worn surface
Summary
Industries have been constantly seeking environmentally friendly and economical lubricants in an attempt to reduce energy waste caused by friction. Friction mineral powders containing silicates, such as serpentine [12, 13] and PAL [14], can be used as self-lubricating materials and added to lubricant oils to form a selfrepairing film with a certain thickness on the metal sliding surfaces. This self-repairing film is a hard and protective film formed by oxide [15]. The sliding contact surfaces are analyzed after the experiment to determine the composition of the tribofilm when the lubricant additive is added Based on these results, the tribological behavior is described and a potential lubrication mechanism of the nanoplatelets is proposed
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