Reactivity of alkylated phosphorothionates with steel: a tribological and surface‐analytical study

Abstract

Phosphorothionates are anti‐wear lubricant additives and potential replacements for zinc dialkyldithiophosphates. In this study, ball‐on‐disc tests have been carried out combinatorially under extreme pressure (EP) conditions (100–350 MPa at 10 N load). The tests were performed in oil containing triphenyl phosphorothionates substituted with alkyl chains of different lengths. Imaging, small‐area and angle‐resolved X‐ray photoelectron spectroscopy were performed following the tribotest to probe the modification, removal and growth of the surface film. The films were composed, depending on the test conditions, of (i) iron phosphate, (ii) iron phosphates with sulphates or (iii) a mixture of iron phosphates with sulphides and sulphates. With increasing load, the dimensional wear coefficients decreased. Upon increasing temperature from 30 to 150°C, the wear became more severe. These findings suggest the formation of a tribochemical film with some EP performance, despite the severe tribological test conditions applied in this work. Copyright © 2008 John Wiley & Sons, Ltd.

Reactivity of Triphenyl Phosphorothionate in Lubricant Oil Solution

“…Recently, the reactivity of alkylated TPPTs with airoxidized steel was investigated in our group [25,26]. In the absence of mechanical stress, the phosphorothionate molecules adsorbed on the substrate at low temperature (303-353 K), as described by Koyama et al [27].…”

“…metal-free) additives, such as organosulfur compounds [6], phosphates [6][7][8][9][10][11][12][13][14][15][16], amine phosphates [12], phosphites [11,[17][18][19], phosphorothionates [12][13][14][20][21][22][23][24][25][26], and dithiophosphates [12,21,22,24].…”

“…Several analytical techniques have been employed to characterize the reaction layers, such as X-ray photoelectron spectroscopy (XPS) [7,12,14,25,26], X-ray absorption spectroscopy (XAS) [13,[21][22][23][24], X-ray photoelectron emission microscopy (X-PEEM) [24], scanning electron microscopy (SEM) [20,21], Fourier transform infrared spectroscopy (FT-IR) [7,14,16], Auger electron spectroscopy (AES) [8-10, 14, 17, 18], and atomic force microscopy (AFM) [22]. Najman et al investigated the thermal films and tribofilms formed by phenyl phosphates on steel [13].…”

Substituent Effect on the Reactivity of Alkylated Triphenyl Phosphorothionates in Oil Solution in the Presence of Iron Particles

“…In the following section a reaction mechanism for alkylated TPPTs will be proposed. The fact that the reaction layers analysed in the present work differ from those investigated in the previous study carried out in our group with the same molecules can be ascribed to the more severe experimental conditions employed here: the heating temperature was 473 K (compared to 423 K in [26]) and the duration of the heating was extended to 72 h (compared to ca. 5 h in [26]).…”

“…The surface reactivity of alkylated phosphorothionates (triphenyl phosphorothionates (TPPTs) substituted with alkyl chains of different lengths) with air-oxidized steel was also investigated in our group [25,26]. The activation temperature for the thermal decomposition of TPPTs was found to be around 423 K. At 423 K a thin reaction layer, consisting of short-chain polyphosphates and oxidized sulphur species, was formed in the non-contact region of airoxidized steel (thickness of the oxide layer: 2.7 ± 0.2 nm) after ca.…”