The Dispersibility And Lubrication Properties Of Molybdenum Disulfide/Sericite In Their Catalytically Synthesized Easter Oils

Nano molybdenum disulfide(nano-MoS₂)is a potential lubricant additive in engine oil.However,the inferior dispersibility of nano-MoS₂ in base oil limits its application in engine oil.The catalyst-then-lubricant strategy is developed to cope with the above problem.The synthetic reactions of three ester base oils with different molecular weights using nano-MoS₂/sericite(S-MoS₂/sericite)compound as catalyst were selected as the objects.The catalytic esterification activity of S-MoS₂/sericite and its dispersion behavior in the product ester were studied.Tribological properties of the S-MoS₂/sericite catalyst retained in the product ester(act as a lubricant after catalysis)were systematically investigated.Firstly,a hollow spherical S-MoS₂/sericite compound was employed to catalyze the esterification of adipic acid and n-butanol at 145?.The product was determined to be dibutyl adipate by FTIR and NMR characterization,indicating that S-MoS₂/sericite with catalytic esterification can be used as a catalyst for the synthesis of ester base oils.After the reaction,the S-MoS₂/sericite catalyst can be retained in the product ester,and the dispersion system can be stably preserved for at least 45 days.The inductively coupled plasma mass spectrometer(ICP-MS)results show that the content of S-MoS₂/sericite in the dispersed system is?400 mg/L.With the extension of resting time,the lubrication performance does not decrease significantly.Compared with the pure base oil,the average friction coefficient and wear rate of the dispersed system after resting time for 45 days can be reduced by?16%and 72%respectively.At high load and low speed,the lubrication mechanism is mainly to form the tribofilm containing MoS₂at the furrow and gully of the friction surface,while S-MoS₂/sericite at low load and high speed can be embedded on the softer friction pair surface to resist friction shear.Then di-n-octyl sebacate(DOS)was synthesized via S-MoS₂/sericite catalyzed esterification of sebacic acid with n-octanol.The infrared spectrum shows that S-MoS₂/sericite can also catalyze the esterification of sebacic acid and n-octanol.The lubrication properties of commercial DOS,DOS synthesized by esterification with and without surface functionalized S-MoS₂/sericite were compared by high frequency reciprocating friction and wear testing machine.The results show that the average wear rate on the steel balls are 46.44?m³/N·m,20.21?m³/N·m,22.61?m³/N·m,and the friction coefficient are 0.181,0.141,0.082,respectively.In the friction process,the S-MoS₂/sericite compound mainly participates in the formation of tribofilm to improve the anti-wear and anti-friction properties of the friction pair surface.The surface functionalization can improve the dispersion stability of the S-MoS₂/sericite compound in its catalytically synthesized DOS,and increase the content of MoS₂ in the formed tribofilm,so that the lubrication performance of the dispersion system can be further enhanced.Finally,the catalyzed behavior of S-MoS₂/sericite for synthesizing poly(propylene glycol)adipate and their dispersibility and tribological properties in the resulting ester were investigated.Infrared spectrum characterization results show that the product ester had a strong ester group absorption peak at 1727 cm^-1.The kinematic viscometer testing results show that the oil synthesized by S-MoS₂/sericite catalyst had higher viscosity and relatively larger molecular weight than that of the oil synthesized without catalyst,suggesting S-MoS₂/sericite has high catalytic esterification activity.Raman and ICP-MS results show that the S-MoS₂/sericite compound is dispersed in the product poly(propylene glycol)adipate ester,and the S-MoS₂/sericite has the best dispersion performance in the oil prepared with alcohol-acid ratio of 1:2.4 under the vacuum condition.The tribological properties of the above oil samples prepared with and without S-MoS₂/sericite catalyst was tested.It was found that the wear scar diameter decreased by 19.8%,the wear area decreased by 93.6%,and the friction coefficient decreased by 14.5%.The results indicate that S-MoS₂/sericite not only serves as the catalytic effect,but also acts as a lubricating additive,which plays an anti-wear and friction-reducing role.In this paper,three different systems were catalytically synthesized using S-MoS₂/sericite,which not only proves that S-MoS₂/sericite has a certain catalytic ability,but also shows the desirable dispersibility in synthetic ester oil and excellent lubrication performance in the tribological test.The research results have theoretical significance and practical application value in the field of MoS₂ catalysts,the application field of sericite,and ester synthetic base oil.This study provides a new idea for solving the dispersion problem of MoS₂ in the base oil,which realizes dispersion at the same time as catalysis.However,the dispersion amount of nano-MoS₂ and the stability of the dispersion system need to be further improved.