Tribocatalytic behaviour of a TiO₂ atmospheric plasma spray (APS) coating in the presence of the friction modifier MoDTC: a parametric study

Abstract

Tribocatalytic behaviour of TiO2 APS coatings in presence of MoDTC additive under boundary lubrication conditions – decomposition mechanism

Mo(VI) dithiocarbamate with no pre-existing Mo–S–Mo core as an active lubricant additive

“…The absence of core sulfur in molecule MoDTC also rules out (at least in the initial stages) the chemical degradation mechanism proposed by Grossiord et al [8] where only sulfur atoms present in the core of the molecule contribute to the MoS2 generation. The necessary involvement of the sulfur atoms in the ligands of MoDTC 1 remains compatible with at least two proposed mechanisms: the formation of a Linkage Isomer -MoDTC [11,12], or the cleavage of carbonsulfur bonds of the ligand [7,16]. Then, MoSx intermediate products seems needed before generating well-organized MoS2 lamellar sheets during friction as it was proposed previously [7,26].…”

“…Even if the mechanism of action of MoDTC has been widely studied, [7][8][9][11][12][13][14][15] [11,12] or by cleavage of carbon-sulfur bonds of the ligand, schematized as (R2NC) [(S2Mo(O)(µ-S)2Mo(O)S2)] (CNR2) [7,16]. All these approaches suggest that core [MonSm] fragments called MoSx intermediate products [7] are needed at some stage in generating well-organized MoS2 lamellar sheets during friction.…”

Tribocatalytic Reaction Enabled by TiO2 Nanoparticle for MoDTC-Derived Tribofilm Formation at ta-C/Steel Contact

“…Onodera et al [37] reported that MoDTC transformed into a bridging isomer of MoDTC (Li-MoDTC) at moderate temperatures. Deshpande et al [38,39] reported that the decomposition of MoDTC was accelerated by the catalysis of a TiO 2 atmospheric plasma-spray coating.…”

Tribocatalysis mechanisms: electron transfer and transition

“…With the oxygen vacancies as the reductive species, these decomposed MoDTC into MoS 2 . 74 Based on this work, the team explored the tribological performance of lubricants containing nano-TiO 2 and MoDTC in steel–steel friction layers. The same reaction mechanism was used, and the generated MoS 2 was the main reason for reducing friction.…”