Method for the determination of the oxidative stability of a lubricating fluid

1. A method for the determination of the oxidative stability of a lubricating fluid, comprising:

introducing a sample of the lubricating fluid under test in an reaction cell;

introducing catalytic amounts of a catalyst to the reaction cell;

heating the cell to the oxidation temperature of the lubricating fluid and maintaining this temperature;

delivering a gas comprising oxygen at constant flow rate through the cell over the course of the reaction;

delivering a gas comprising nitrogen dioxide at a constant flow rate through the cell for a specified time;

applying and maintaining a specified vacuum on the reaction cell such that the reaction cell is maintained under a reduced pressure ranging from 0.05 to 0.07 MPa;

allowing the mixture to react for a specified time;

measuring the viscosity of the oxidized lubricating fluid.

2. The method according to claim 1 wherein the oxidation temperature is in the range of 160° C. to 180° C.

3. The method according to claim 1 wherein the specified time for allowing the mixture to react is in the range of 30 to 50 hours.

4. The method according to claim 1 , wherein the nitrogen dioxide flow is in the range of 0.15 to 0.18 milliliters per hour over 11 to 13 hours.

5. The method according to claim 1 , wherein the delivering of the gas is performed under a reduced pressure.

6. The method according to claim 1 , wherein the total amount of nitrogen dioxide delivered to the reaction cell is in the range of 1 to 2% by weight based on the total amount of lubricating fluid at the start of the test.

7. The method according to claim 1 , wherein the Mini-Rotary Viscosity of the lubricating fluid is measured according to ASTM D 4684.

8. The method according to claim 1 , wherein the increase of the kinematic viscosity at 40° C. of the lubricating fluid is measured according to ASTM D 445.

9. The method according to claim 1 , wherein the lubricating fluid is an engine oil lubricant or a transmission or a hydraulic fluid.

10. The method according to claim 1 , wherein flow of the gas containing oxygen is in the range of 180 to 190 milliliters per minute throughout the reaction.

11. The method according to claim 10 wherein the reduced pressure of the specified vacuum is in the range of 0.061 to 0.063 MPa.

12. The method according to claim 1 , wherein the heating of the cell is performed under a reduced pressure.

13. The method according to claim 12 wherein the reduced pressure of the specified vacuum is in the range of 0.061 to 0.063 MPa.

14. The method according to claim 12 wherein the reduced pressure of the specified vacuum is in the range of 0.057 to 0.064 MPa.

15. The method according to claim 1 , wherein iron ferrocene is used as catalyst.

16. The method according to claim 15 , wherein iron ferrocene is added to the reaction mixture at 10 to 20 ppm based on the lubricating fluid charge.