Study on the mechanism of rapid formation of ultra-thick tribofilm by CeO2 nano additive and ZDDP

Abstract

CeO2 nanoparticles are potential anti-wear additives because of their outstanding anti-wear and load-bearing capacity. However, the shear-sintering tribo-film formation mechanism of oxide nanoparticles limits the tribo-film formation rate and thickness greatly. In this study, by compounding with zinc dioctyl dithiophosphate (ZDDP), ultra-fine CeO2 nanoparticles modified with oleylamine (OM) can quickly form 2 µm ultra-thick tribo-film, which is 10–15 times thicker than that of ZDDP and CeO2, respectively. The ultra-thick tribo-film presents a nanocomposite structure with amorphous phosphate as binder and nano-CeO2 as filling phase, which leads to the highest loading capacity of composite additives. The results of adsorption experiments tested by dissipative quartz crystal microbalance (QCM-D) showed that the PB value of additive has nothing to do with its equilibrium adsorption mass, but is directly proportional to its adsorption rate in 10 s. The compound additive of CeO2 and ZDDP presented the co-deposition mode of ZDDP monolayer rigid adsorption and CeO2 viscoelastic adsorption on the metal surface, which showed the highest adsorption rate in 10 s. It is found that the tribo-film must have high film forming rate and wear resistance at the same time in order to achieve super thickness. Cerium phosphate was formed from ZDDP and CeO2 through tribochemistry reaction, which promotes the formation of an ultra-thick tribo-film with nanocomposite structure, which not only maintains the low friction characteristics of CeO2, but also realizes high PB and high load-carrying capacity.

High Friction Mechanism of ZDDP Tribofilm Based on in situ AFM Observation of Nano-Friction and Adhesion Properties

“…In our experiments, the friction coefficient after 600 cycles for the base oil and the ZDDP solution were approximately 0.03 and 0.06, respectively. These coefficients are significantly lower than those observed at the macroscale (approximately 0.10 to 0.20), corresponding to the boundary-tomixed lubrication conditions [4,[10][11][12][13][14][15][16][17]. The diplomacy with the macroscale sliding tests is also related to the differences in the contact pressure.…”

“…On the other hand, ZDDP tribofilms also have the disadvantage of increasing friction, although tribofilms have high anti-wear properties [4,9,10,[11][12][13][14][15][16][17][18]. The field targeting high friction of ZDDP tribofilm in the mixed lubrication was studied extensively [4,9,10,17,19].…”

A dual-responsive microemulsion with macroscale superlubricity and largely switchable friction

“…In addition, given that surfactants without [CeCl 4 ] À cannot result in ultralow friction under the same tribological conditions, and hence, the exceptional lubrication should mainly stem from reactions of the Ce(III)-containing coordination anion, which led to the formation of CeO 2 products having been testified to exhibit potent lubricity. [42][43][44] The absorption bands completely vanished at 50 1C, indicating that the tribochemical reactions were suppressed, which consequently gave rise to the significantly deteriorated lubrication of the DDACe/EG/n-hexane/water mixture.…”

Synergistic tribological effect between polyisobutylene succinimide-modified molybdenum oxide nanoparticle and zinc dialkyldithiophosphate for reducing friction and wear of diamond-like carbon coating under boundary lubrication

“…base (HSAB) principle [43][44][45][46], the as-released MoO 3 exhibits strong interaction with polyphosphate (the decomposed product of ZDDP), which contributes to the formation of the composite tribofilm with amorphous polyphosphate as the binder and MoO 3 nanoparticle as the filling phase. Moreover, the easily sheared small MoS 2 with a low hardness is embedded in polyphosphate matrix during the sliding process, which also contributes to the formation of the composite tribofilm [45].…”