Improved tribological properties, thermal and colloidal stability of poly-α-olefins based lubricants with hydrophobic MoS2 submicron additives

HYPOTHESIS

Newtonian liquids, usually used as base oil lubricants, exhibit low viscosity under extreme thermal conditions, needed for the functioning of wind turbines. This is directly affecting the colloidal stability and the tribological properties of the formulations containing additives, such as MoS₂. Here, it was hypothesized that the surface hydrophobization of MoS₂ particles will allow for an increased colloidal stability of the resulting formulations, for temperatures as high as 80 °C.

EXPERIMENTS

The antifriction properties and the thermal stability of the designed formulations were determined on submicron MoS₂ particles dispersed in poly-α-olefins (PAO) base oils of different dynamic viscosities (from 32 to 1650 mPa·s at 25 °C). The submicron particles of MoS₂ (300-500 nm in diameter) were synthesised by a simple one-pot solvothermal method under mild conditions. The resulting particles were hydrophobized in situ in PAO base oils using alkyltrichlorosilane grafting agents with two chain lengths (C8 and C18).

FINDINGS

The covalent grafting of alkylsilanes through Mo-O-Si bonds was confirmed by DFT calculations and FT-IR measurements. Turbiscan optical analysis revealed that thermal and colloidal stabilities can be significantly improved depending on oil viscosity and chain length of the grafting agent. The formulations in the PAO65 oil remained highly stable (TSI < 1), even at 80 °C. Herein, we demonstrate the impact of hydrophobization degree on the tribological properties of the lubricants, which, importantly, could reach ultra-low friction coefficients, less than 0.02.

Low solvothermal synthesis and characterization of hollow nanospheres molybdenum sulfide

Hollow nanospheres of molybdenum disulfide have been synthesized by a novel solvothermal method under low temperature (180 degrees C). These nanomaterials were characterized by X-ray diffraction (XRD), Fourier transformation infra-red spectroscopy (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM, HRTEM) and X-ray Photoelectron Spectroscopy (XPS). A mechanism for the synthesis reaction is tentatively proposed and discussed.

Easy extrusion of honeycomb-shaped monoliths using Moroccan natural clays and investigation of their dynamic adsorptive behavior towards VOCs

In the present work, honeycomb-shaped monoliths were easily extruded using local natural clays without the need of chemical binders. This finding allows significant cost reduction, in terms of not only additives and solvents but also the energy consumption required for their elimination by thermal treatment. The extruded monoliths were subject to mechanical strength testing in addition to the study of their thermal behavior, structural and textural properties. Moreover, one of their potential uses as VOCs adsorbents was evaluated in comparison with conventional packed bed by investigating their dynamic adsorptive and desorption behavior towards a model VOC of o-xylene type.