posted on 2024-01-03, 06:45authored byTuong
Ly Kiet Dao, Anh Kiet Tieu, Bach Hoang Tran
This study focuses on the synthesis and investigation
of four organophosphate-intercalated
CoAl-LDHs as additives for oil lubricants. Phosphate esters have been
well-known for their excellent antiwear properties in automobile applications.
On the other hand, layered double hydroxide (LDH) has a unique lamellar
structure that can contain anionic species that can be released under
certain conditions. The successful intercalations of various organophosphates,
including methyl phosphate (C1P), isopropyl phosphate (C3P), phenyl
phosphate (C6P), and dodecyl phosphate (C12P), into CoAl-LDH were
achieved. Ultimately, the C6P-LDH demonstrated exceptional antiwear
performance, reducing friction and wear loss by 25% and 69%, respectively,
compared to PAO-4 base oil. Interestingly, the C6P tribofilm shows
two distinct regions with different colors under an optical microscope.
Thorough characterizations of the two regions of interest were conducted
via Raman spectroscopy, scanning transmission electron microscopy,
energy dispersive X-ray spectroscopy, and cryo-electron energy loss
spectroscopy techniques and demonstrated that the blue tribofilm pads
consisted of mixed metallic oxides and phosphates, while the gray
pads were rich in metallic cobalt, which was unexpected for tribofilm
formed in situ during lubrication under ambient atmosphere.
The thick oxide-phosphate layer is crucial for preventing wear loss.
Additionally, a thin iron oxide layer at the steel interface strengthens
the tribofilm adhesion to the steel base. The tribofilm formation
mechanism was discussed and proposed. The influence of LDH dispersibility
on the tribological behaviors was also discussed.