Weimin Li

Tribological Study of Boron-Containing Soybean Lecithin as Environmentally Friendly Lubricant Additive in Synthetic Base Fluids

Environmentally friendly boron-containing soybean lecithin (BSL) was synthesised. Constant temperature and humidity box was applied to evaluate the hydrolytic stability of the novel lubricant additive. The friction-reducing, anti-wear, and extreme pressure performance of BSL in synthetic base fluids were studied by an optimol SRV-I oscillating reciprocating friction and wear tester and four-ball tester. The hydrolytic resistance test results reveal that BSL possesses good hydrolytic stability. Tribological tests show that the friction-reducing performance of BSL in A51 is inferior to PAO10. The incorporation of BSL in synthetic basestock can dramatically reduce the wear volume of the lower steel disc under different test conditions. BSL can also enhance the load-carrying capacities of the synthetic base fluids. Morphology and chemical composition of the wear surface were characterized by scanning electron microscope and X-ray photoelectron spectroscopy. The results indicated that excellent tribological performance of the BSL can be attribute to the formation of chemisorption and chemical reaction protecting films composed of Fe2O3, iron polyphosphates, organic amines, and BN, etc.

Tribological properties of castor oil tris(diphenyl phosphate) as a high-performance antiwear additive in lubricating greases for steel/steel contacts at elevated temperature

Castor oil tris(diphenyl phosphate) (CODP) was synthesized using an environmentally friendly and renewable resource – castor oil, and its tribological properties were evaluated in lithium 12-hydroxystearate greases (LHG) and lithium complex greases (LCG) at 150 °C. The tribological behaviors of the additive for LHG and LCG application in steel/steel contacts were evaluated on an Optimol SRV-IV oscillating reciprocating friction and wear tester as well as on a MS-10J four-ball tester. The worn steel surface was analyzed by a JSM-5600LV scanning electron microscope and a PHI-5702 multifunctional X-ray photoelectron spectrometer. The results indicated that CODP as the additive could effectively reduce the friction and wear of sliding pairs in the two base greases. The tribological performances were also better than the traditional used zinc dialkyldithiophosphate (ZDDP) based additive package in LHG and also in LCG. Boundary lubrication films composed of Fe(OH)O, Fe3O4, FePO4 and compounds containing P–O bonds were formed on the worn surface, which resulted in excellent friction reduction and antiwear performance.

Antioxidant synergism between synthesised alkylated diphenylamine and dilauryl thiodipropionate in polyolefin base fluid

An oil-soluble additive alkylated diphenylamine (ADPA) was synthesized. The antioxidant activities of ADPA and dilauryl thiodipropionate (DLTDP) as well as their mixtures in PAO10 were evaluated by rotary bomb oxidation test, pressurized differential scanning calorimetry, hot oil oxidation test, and thermogravimetry. All the tests showed that the anti-oxidation stability of ADPA was significantly improved with the addition of DLTDP. The kinetic parameters of thermal-oxidative process were also evaluated using the Kissinger method which has been widely used for the determination of activation energy and pre-exponential factor. The results indicated that ADPA could significantly improve the activation energy of PAO10 and reduce the rate of the thermal-oxidative reaction when combining with DLTDP antioxidant. All these results demonstrated that the combination of ADPA and DLTDP revealed a good synergistic effect and could effectively enhance the thermal-oxidation stability of PAO10. The proposed mechanism of the inhibition involved a synergy between ADPA and DLTDP.

Reinforcing effect on the tribological behaviour of nanoparticles due to a bimodal grain size distribution

In this study, two kinds of calcite calcium carbonate nanoparticle additives (CN), with a grain size of ca. 30 nm and 80 nm, respectively, were synthesized via the carbonation method. Then, a series of additives were prepared through tuning the grain size distribution, and the corresponding tribological performances were also carefully investigated. Compared to the uniform size additives, the performance of the additives with a bimodal grain size distribution was obviously improved and the application range was further extended. Moreover, it can be observed that CN with a large grain size could improve tribological behavior under high frequency conditions, whereas the CN with a small grain size determined the load bearing capacity. The corresponding lubrication mechanisms were also investigated according to the characterization results of the wear scar surface, such as the morphology, composition and microstructure. The results indicated that a continuous protective film was formed on the contact surface and the corresponding mechanical properties determined the final lubricity. The enhancement of the tribological performance can be attributed to the improved toughness of the protective film, due to the reinforcing effect of the bimodal grain size distribution.

New insight to the tribology-structure interrelationship of lubricating grease by a rheological method

By controlling the heat-treatment process, three types of lithium greases with different thickener fiber morphologies were synthesized via the saponification reaction. With increasing the cooling rate, the dimension of the thickener fiber decreased. The relationship between microstructure and tribological performance of the lubricating greases was investigated via a rheological method. The results indicated that the fiber dimension determined the level of physical entanglement and the evolution of fiber network in the friction process, further influencing the final lubricity. The grease with the large fiber dimension displayed good tribological performance under low frequency and high load conditions due to its large-scale strongly crosslinked structure. In addition, the grease with the small fiber dimension yielded a low level of fiber physical entanglements and displayed low structure strength and fast response in the rheological test. It could obviously improve the tribological performance under high frequency conditions. Through tuning the microstructure of the thickener fiber according to the lubricating conditions, the tribological performance could be obviously improved.

Thermal decomposition kinetics and anti-oxidation performance of commercial antioxidants

The thermal stability of 2, 6-Di-tert-butyl-4-methylphenol (T501) and N-Phenyl-1-naphthylamine (T531) was comparatively investigated using thermogravimetry(TG)/derivative thermogravimetry under air atmosphere. Activation energies of the corresponding thermal decomposition process were evaluated by Flynn–Wall–Ozawa and Kissinger methods. Pressurized differential scanning calorimetry and TG methods were also employed to study their antioxidant performance in different kinds of lubricating oils. The thermal analysis and kinetic study showed that the thermal stability of T531 was superior to that of T501. The oxidation tests indicated that T531 exhibited better anti-oxidation property than T501 in the tested oils. All the results demonstrated that T531 was a more efficient antioxidant with outstanding thermal stability and oxidation resistance.

Study of soybean lecithin as multifunctional lubricating additives

Purpose – The purpose of this paper is to study the antirust, tribological performance and anti-wear (AW) mechanism of the of soybean lecithin (SL) as a kind of multifunctional lubricant additive. Design/methodology/approach – As a kind of multifunctional lubricant additive, the antirust performance of SL was tested according to ASTM D 665, and meanwhile, its tribological performances were also evaluated by Optimol SRV-I oscillating reciprocating friction and wear tester and four ball tester. The worn steel surfaces were investigated by scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS). Findings – The results showed that the SL exhibited excellent antirust properties in different base stock, and could effectively improve the AW and extreme pressure (EP) performances. The results of SEM and XPS indicated that a protective film was formed between steel-steel friction pair during the tribological test. Originality/value – This paper first investigated the antirust properties and t...

Viscosity modification of lubricating oil based on high-concentration silica nanoparticle colloidal system

ABSTRACT In this study, colloidal systems with SiO2 nanoparticle as viscosity modifier additive were synthesized in the lubricating oil via an in situ Stober sol-gel method. The fluid characters of lubricating oil and viscosity variation were carefully investigated via rheological methods. The results showed that the lubricating oil transformed from Newtonian fluid to non-Newtonian fluid with increasing the concentration of nanoparticles, and smaller particles displayed better thickening effect toward lubricating oil. For the system with highly concentrated nanoparticle (20 wt%), the rheological behavior mainly depends on the size of nano-SiO2. The lubricating oil with smaller nano-SiO2 particles displayed higher structural strength and response rate, resulting in good recoverability after high-speed shear. The viscosity changed with temperature and also displayed a thermo-responsive behavior, which significantly alleviated the effect of shear thinning on the viscosity under high temperature. This study presented a new strategy for effectively tuning the fluid characters and modifying the viscosity of lubricating oils by adding highly concentrated inorganic nanoparticles. GRAPHICAL ABSTRACT

Effect of alkylated diphenylamine on thermal-oxidative degradation behavior of poly-α-olefin

An oil-soluble antioxidant, alkylated diphenylamine (ADPA), was prepared by alkylation of diphenylamine. The influence of ADPA on the thermal-oxidative stability of poly-α-olefin (PAO8) was evaluated by thermogravimetry (TG). For comparison, the thermal-oxidative stability of PAO8 with zinc dialkyl dithiophosphate (ZDDP) was also investigated. Activation energy (Ea)of the corresponding thermal-oxidative degradation process was evaluated by the Flynn-Wall-Ozawa (FWO) and Kissinger-Akahira-Sunose (KAS) methods. To demonstrate the reliability of the kinetic study, the antioxidant performance of ADPA and ZDDP in PAO8 was also studied by the pressure drop (PDT) and accelerated oxidation (AOT) tests. The results indicate that ADPA has better antioxidant ability than ZDDP in increasing the Ea value and enhancing the oxidative stability of PAO8. Good correlation between the applied test methods was established.

Tribological properties of polyol-ester-based lubricants and their influence on oxidation stability

Unlike oxidative degradation of lubricants, tribology-induced degradation is rarely studied. In this work, the tribological performance and oxidative stability of ester-based lubricants were evaluated before and after tribological testing. Results showed that the tribological performances of base oils are highly dependent on the lubricant formulation and test conditions. Tribological processes could cause detrimental effects on oxidative stability even under moderate conditions. The addition of antiwear additives seems to effectively inhibit the chemically breakdown of esters by forming a protective film. Mechanical shearing, high temperature in contact zones, catalytic effect of nascent surface, wear debris, as well as self- catalysis are the major reasons that are responsible for the oxidative deterioration of the lubricant after tribological testing.