Effect of Lubricant Additives on Tribochemical Decomposition of Hydrocarbon Oil on Nascent Steel Surfaces

Abstract

A nascent surface has high activity to catalyze the decomposition of lubricants under boundary lubrication conditions. The effects of sulfur-containing, nitrogen-containing, phosphorus-containing additives and phosphatecontaining ionic liquid were investigated on the decomposition of synthetic hydrocarbon oil (multialkylated cyclopentane, MAC). The decomposition processes of the lubricants on the nascent surface of bearing steel AISI 52100 were investigated using a ball-on-disk friction tester in a vacuum chamber with a quadrupole mass spectrometer. Three parameters related to the decomposition process were observed: the induction period for the decomposition, the desorption rate of gaseous products, and the critical load for the activation of the decomposition. The order of efficiency of additives in extending the induction period was: sulfur-containing additive (S)＜nitrogen-containing additive (N)＜phosphorus-containing additive (P)＜phosphate-containing ionic liquid (P-IL). The order of efficiency in increasing the critical load was: N＜S＜P＜P-IL, and the order of efficiency in decreasing the decomposition rate was: N＜S＜P＜P-IL. These results suggest that additives which can form iron salts (such as iron phosphate and iron sulfide) will deactivate the nascent surface, decreasing the decomposition rate and increasing the critical load.

Development of a novel in-situ technique for hydrogen uptake evaluation from a lubricated tribocontact

“…This is in line with previous in-situ measurements that showed emitted hydrogen from tribological contact only happens when sliding occurs on the surface [5,16]. It has also been revealed that lubricant decomposition rate is directly related to sliding velocity and the applied load [13,14,16]. Molecular dynamics simulations [12] have also shown that if a lubricant film is subjected to shearing between two sliding surfaces, both hydrogen diffusion and hydrogen adsorption on the metal surfaces will be induced.…”

“…This will cause serious problems in critical components such as bearings [4][5][6][10][11][12][13][14][15][16]. Uyama et al [6] and Ciruna et al [3] observed that hydrogen content in the AISI 52100 bearing steel is one of the prime reasons for reduced bearing life.…”

“…Special efforts have been made so far regarding in-situ monitoring of tribological hydrogen gas evolution [5,14,16,21]. In these research works, quadrupole mass spectrometer techniques were used in high vacuum or in a controlled gaseous atmosphere to analyse the products from tribochemical reactions occurring on the rubbing surface [5,14,16].…”

“…In these research works, quadrupole mass spectrometer techniques were used in high vacuum or in a controlled gaseous atmosphere to analyse the products from tribochemical reactions occurring on the rubbing surface [5,14,16]. Lu et al [14] investigated the effect of different additives on oil decomposition under friction conditions. They showed that phosphatecontaining ionic liquid additives are more efficient in preventing the decomposition of lubricants in comparison with additives containing sulphur, nitrogen and phosphorus.…”

“…However, the results of these experiments in such controlled atmospheres often miss some critical aspects of hydrogen generation and permeation if they are used to study the hydrogen embrittlement phenomenon. Firstly, one of the sources of hydrogen is believed to be attributed to oxidative decomposition of the lubricant on the fresh metal surface [14,16], but doing the experiment in a vacuum chamber delays the oxidation of fresh surface and increases the hydrogen generation compared to real working condition. Secondly, these techniques only detect non-absorbed hydrogen.…”