AQUEOUS LUBRICATING COMPOSITION COMPRISING MoS2 NANOSHEET

Abstract

The present invention relates to a lubricating composition comprising: water, especially purified water, for example ultrapure water, demineralized water, osmotic water, deionized water; glycerol; nanosheets of h-MoS2, wherein the active content of h-MoS2 nanosheets is comprised between 0.01 and 0.07 wt %, preferably between 0.02 to 0.06 wt %, based on the total weight of the lubricating composition, wherein, the nanosheets of h-MoS2 are obtained in-situ in the lubricating composition by liquid-phase exfoliation of bulk MoS2 particles water.

Claims

1. A lubricating composition comprising: water; glycerol; nanosheets of h-MoS.sub.2, h referring to the hexagonal phase of MoS.sub.2, wherein the active content of h-MoS.sub.2 nanosheets is comprised between 0.01 and 0.07 wt %, based on the total weight of the lubricating composition, wherein, the nanosheets of h-MoS.sub.2 are obtained in-situ in the lubricating composition by liquid-phase exfoliation of bulk MoS.sub.2 particles.

2. Composition according to claim 1 wherein the active content of h-MoS.sub.2 nanosheets is comprised between 0.02 to 0.06 wt %, based on the total weight of the lubricating composition.

3. The composition of claim 1 comprising at least 20 wt % of glycerol, based on the total weight of the lubricating composition.

4. The composition of claim 1 wherein the water is purified water.

5. The composition of claim 1 comprising more than 35 wt % of water, based on the total weight of the lubricating composition.

6. The composition of claim 1 wherein the liquid phase exfoliation is carried out in reduced time from 4 to 8 hours.

7. The composition of claim 1 wherein the liquid phase exfoliation is followed by centrifugation carried out during 1 to 4 hours at 1000 to 10000 rpm.

8. A process for preparing the lubricating composition claim 1 comprising the following steps: addition of bulk MoS.sub.2 particles in a water solution comprising glycerol; liquid-phase exfoliation of the bulk MoS.sub.2 particles; centrifugation to remove unexfoliated bulk MoS.sub.2 particles.

9. (canceled)

10. (canceled)

11. A process for reducing wear and friction on mechanical parts of a mechanic system comprising putting the mechanical parts of the mechanic system in contact with the lubricating composition according to claim 1.

12. The process of claim 11 for reducing wear and friction of gear, bearing and transmission.

Description

EXAMPLES

Pin-On-Disk Tribometer Measurements

[0099] The lubricating performance of formulations was investigated using a pin-on-disk high temperature tribometer (CSM Instruments THT).

[0100] The measurements were carried out in the following conditions: [0101] Load values: 5-10 N; [0102] Sliding speeds: 1-4 cm/s; [0103] Temperature: measurements were carried out at room temperature (25? C.); [0104] Disk surfaces: the lubricants were tested on steel 100Cr6 disks from Optimal Instruments (24 mm diameter?7.9 mm thick) with a Rockwell C hardness according to the supplier of 60?2 HRC and an average roughness Ra=0.046 ?m?0.003 ?m, measured hardness was 66?1 HRC, higher than that given by the supplier [0105] Ball properties: steel 100Cr6 balls (6 mm diameter) purchased from Anton Paar were used for the pin-on-disk tribology measurements with a hardness according to the supplier of 60-66 HRC and an average roughness Ra<0.032 ?m. Measured hardness was 68?1 HRC higher than that given by the supplier.

Wear Analysis

[0106] The surface of steel 100Cr6 disks and balls after the pin-on-disk tribology measurements was examined by optical microscopy (Leica DM4000M) and confocal microscopy (Leica DCM3D) to evaluate wear of both contacting surfaces lubricated by the different formulations. The ball wear volume loss was estimated from the radius of the wear trace using the equation to calculate the volume of a spherical cap.

Stability

[0107] Stability refers to the time without observing sedimentation and preserving tribological performance.

Example 1: Preparation of Lubricant Composition

[0108] Aqueous solution of MoS.sub.2 nanosheet were produced by liquid-phase exfoliation of bulk micron-sized MoS.sub.2 powder (4 mg/ml) (99%, Acros Organics) in certain volume of aqueous solution of glycerol using a high-power tip sonicator (Dr. Hielscher UP 400S at the highest amplitude and frequency) for times ranging from 4 to 8 hours. Volumes used varied from 30 to 100 mL. After removing unexfoliated MoS.sub.2 as sediment by centrifugation (Thermo Scientific Sorvall Legend XT, from 1 to 4 hours, at 3500 rpm), nanosized MoS.sub.2 nanosheet are obtained directly dispersed in the aqueous lubricants as a result of the exfoliation process. The final concentration of MoS.sub.2 nanosheets can be tuned by varying the sonication time and centrifugation speed and time in a way that the highest concentrations correspond to large sonication times and low centrifugation speed and time.

Example 2: Tribological Measurements

[0109] The tribological measurements mentioned above are carried out using 1 mL out of a 65 mL sample. The pin-on-disk tests were carried out on 66HRC 100CR6 steel disks under the following conditions: 60? C. temperature, 10N load, 1 cm/s sliding speed and 72 m distance.

TABLE-US-00001 Conditions: 66 HRC Steel100Cr6 disks-60? C.-10N-1 cm/s-72 m Disk Ball wear wear Friction width volume coefficient/ (?m)/ (?m.sup.3)/ % of % of % of reduction reduction reduction with with with respect respect respect Stability tot he to the to the Composition (months) reference reference reference Hydransafe 0.13 309 ? 27 (1.3 ? 0.1) ? 10.sup.6 HFC146? Reference + >5 0% 10 27% 0.02 wt % h-MoS.sub.2 nanosheet Reference + >5 0% 29% 75% 0.06 wt % h-MoS.sub.2 nanosheet Reference + <1 0.08 wt % MoS.sub.2 nanosheet (comparative example)

[0110] The results show a remarkable wear reduction ability of the composition of the invention.