Investigation of the Interaction, Rheological and Tribological Properties of Bis(pinacolato)diboron with Lithium Grease

In this article, Lewis acid–base complex of lithium 12-hydroxystearate (LHS) with diboron compound is formed by the introduction of bis(pinacolato)diboron (B2Pin2) into lithium grease. The interaction between Lewis acid B2Pin2 and Lewis base RCO2− of LHS is characterized by various techniques. Moreover, the rheological and tribological behaviors of the base grease are evaluated at low and moderate temperature. The results indicate that the addition of B2Pin2 can noticeably enhance the rheological property of the base grease because the formation of Lewis acid–base complex is beneficial for improving the soap fiber structure strength, and B2Pin2 could also help reduce the friction and wear of the grease during the sliding process, which likely owing to the boundary lubrication film generated by B2Pin2 adsorption on the rubbing surface and tribochemical reaction between borate esters and steel surfaces. The improvement of mechanical stability and tribological properties is beneficial to increasing the grease service life. Graphical Abstract

Investigation of the Interaction, Rheological and Tribological Properties of Bis(pinacolato)diboron with Lithium Grease During Mechanical Aging

In this article, Lewis acid–base complex of lithium 12-hydroxystearate (LHS) with diboron compound is formed by the introduction of bis(pinacolato)diboron (B2Pin2) into lithium grease. The interaction between Lewis acid B2Pin2 and Lewis base RCO2− of LHS is characterized by various techniques. Moreover, the rheological and tribological behaviors of the base grease are evaluated at low and moderate temperature, and the results indicate that the addition of B2Pin2 noticeably enhanced the rheological, friction-reducing, and anti-wear (AW) properties of the base grease, which likely owing to the fact that the formation of Lewis acid–base complex is beneficial for improving the soap fiber structure strength, helping to prevent the mechanical degradation of the lithium grease during mechanical aging process.

Tribological Properties of Complex Calcium Sulfonate Grease with Ultrafine SiO2/MoS2 Powders

For the development of complex calcium sulfonate grease containing ultrafine SiO2/MoS2 powders with self-reparing performance. On the basis of the dispersion of the nanoSiO2 particles, the effects of particle size,addition amount,load and the mass ratio of nanoSiO2 to ultrafine MoS2 powders on the tribological properties of commercial No.2 complex calcium sulfonate grease were systematically studied by four ball friction and wear tester. The results show that suitable particle size and addition amount of single SiO2 and MoS2 powders can significantly reduce the coefficient of friction (COF) and the wear scar diameter (WSD) of the grease. The composite of nanoSiO2 and MoS2 powder can broaden the load range of base grease and further improve the tribological properties of complex calcium sulfonate grease. When the mass ratio of nanoSiO2 powder to MoS2 powder is 3:7 and the total addition amount is 0.8wt%, the COF and the WSD of the grease are decreased by 53.64% and 27.08%, respectively, compared with the base grease. The two powders in the composite grease have synergy effect for improving the tribological performance and the friction stability of the grease during the process of long friction.

Evaluation of the influence of granulation of hexagonal boron nitride on the lubricity properties of the base grease

The paper presents the tests results of lubricity properties of base greases, containing hexagonal boron nitride (h-BN). To conduct the required tests, a four ball machine was used. This device is commonly used when assessing lubricity properties of oils and greases. The following normative lubricity parameters were defined: welding point Pz [daN], the value of last non-seizing load Pn [daN], seizing at smoothy growing load Pt [daN], as well as the wear limiting capacity load Goz [daN/mm2]. Furthermore, several non-normative tests were completed that covered indication of two parameters making it possible to complete an assessment of lubricity properties of oils. Based on the conducted research, it was found that hexagonal boron nitride is an additive that improves the lubricating properties of the base grease. The best effects of the improvement, taking into account the adopted tribological criteria, were noted for a sample containing 10% (m/m) hexagonal boron nitride with an average grain diameter of 65÷75 nm. It was found that the lower granulation of the additive (h-BN) positively influences the efficiency of the grease lubrication of the base, under the conditions of tests on a four-ball model apparatus. Keywords: tribology, lubricity, boron nitride, greases

Graphene as a nanofiller for enhancing the tribological properties and thermal conductivity of base grease

The addition of graphene-reinforced grease to the mechanical friction surface can effectively reduce the friction coefficient and accelerate heat transportation.

Tribological properties of nanometer Al2O3 and nanometer ZnO as additives in lithium-based grease

Purpose Nanoparticles as the grease additives play an important role in anti-wear and friction-reducing property during the mechanical operation. To improve the lubrication action of grease, the tribological behavior of lithium-based greases with single (nanometer Al2O3 or nanometer ZnO) and composite additives (Al2O3–ZnO nanoparticles) were investigated in this paper. Design/methodology/approach The morphology and microstructure of nanoparticles were characterized by means of transmission electron microscope and X-ray diffraction. Tribological properties of different nanoparticles as additives in lithium-based greases were evaluated using a universal friction and wear testing machine. In addition, the friction coefficient (COF) and wear scar diameter were analyzed. The surface morphology and element overlay of the worn steel surface were analyzed by scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS), respectively. Findings The results show that the greases with nanometer Al2O3 or nanometer ZnO and the composite nanoparticles additives both exhibit lower COFs and wear scar diameters than those of base grease. And the grease with Al2O3–ZnO composite nanoparticles possesses much lower COF and shows much better wear resistance than greases with single additives. When the additives contents are 0.4 Wt.% Al2O3 and 0.6 Wt.% ZnO, the composite nanoparticles-based grease exhibits the lowest mean COF (0.04) and wear scar diameter (0.65 mm), which is about 160% and 28% lower than those of base grease, respectively. Originality/value The main innovative thought of this work lies in dealing with the grease using single or composite nanoparticles. And through a serial contrast experiments, the anti-wear and friction-reducing property with different nanoparticles additives in lithium grease are evaluated.

Effect of nanometer silicon dioxide on the frictional behavior of lubricating grease

Nanometer-silicon dioxide encapsulated in lithium grease is prepared, and the frictional behavior of the lithium grease and nanometer-silicon dioxide–contained lithium grease is compared with respect to the additive content, load, and frictional temperature in this article. The structure and morphology of nanometer-silicon dioxide is characterized by X-ray diffraction and scanning electron microscopy, respectively. Friction and wear tests were conducted on a four-ball friction and wear tester. The morphology of worn steel surface is analyzed by scanning electron microscopy and three-dimensional surface profiler. Results show that the addition of nanometer-silicon dioxide in grease can markedly improve the friction-reducing performance and anti-wear ability of base grease. When the nanometer-silicon dioxide in grease is 0.3 wt%, the friction coefficient and wear scar diameter decrease by 26% and 7% compared with base grease, respectively. The nanometer-silicon dioxide (0.3 wt%)–contained grease exhibits the lowest average friction coefficient at the load of 342 N, which decreases by 39% as compared with that of base grease. The worn surface is quite smooth with few shallow furrows and the wear scar diameter decreases under the lubrication of the grease containing 0.3 wt% nanometer-silicon dioxide. Moreover, it was found that the nanometer-silicon dioxide have been incorporated into the surface protective and lubricious layer by energy dispersive spectrometer analysis.

Influence of Carbon Nanotubes on Conductive Capacity and Tribological Characteristics of Poly(ethylene Glycol-Ran-Propylene Glycol) Monobutyl Ether as Base Oil of Grease

Carbon black (CB) and three kinds of carbon nanotubes (CNTs) including multiwalled CNTs (MWCNTs), carboxyl multiwalled CNTs (CMWCNTs), and single-walled CNTs (SWCNTs) were doped as conductive additives in poly(ethylene glycol-ran-propylene glycol) monobutyl ether (denoted as PAG) to afford conductive greases in the presence of polytetrafluoroethylene (PTFE) as the thickener and acetone as the polar dispersant. The effects of the conductive additives on the conductive capacity and tribological characteristics of the PAG grease were investigated, and the tribological action mechanisms of the conductive additives were analyzed in relation to worn surface analyses by scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS). Results indicate that the SWCNTs can reduce the volume resistivity of the base grease by over 10,000 times. In the meantime, the CB and the three kinds of CNTs as conductive additives can improve the tribological characteristics of the base grease to some extent, and the CNTs are advantageous over the CB in improving the friction-reducing and antiwear abilities of the base grease. The reason lies in that CNTs with a small size and a large specific surface area can be easily adsorbed on sliding steel surfaces to form a surface protective film.