ASTM D5763 Standard Test Method for Oxidation and Thermal Stability Characteristics of Gear Oils Using Universal Glassware
10. Procedure
10.1 Using Test Method D445, determine the viscosity of the oil at 100°C. Record as V2.

10.2 Adjust the heating bath or block to a temperature high enough to maintain the oil in the desired number of oxidation cells at the required temperature of 120 +/- 1°C.

10.3 Place and weigh a 1000-mL beaker on the balance. Zero the tare of the beaker and place the oxidation cell in the beaker. Insert the air delivery tube in the cell. The angled tip of the air delivery tube should rest on the bottom of the oxidation cell. Obtain the weight of the cell and delivery tube. Record as B1.

10.4 Slowly pour 100.00 +/- 0.1 g of oil sample into the oxidation cell which contains the air delivery tube. Obtain the weight of the oil sample, air delivery tube, and oxidation cell, A2.

10.5 Place the oxidation cell containing the oil sample and air delivery tube in the heating block or bath.

10.6 Connect the air delivery tube to the air source from the flowmeter. Adjust the flow of dried air to 3 +/- 0.5 L/h.

10.7 Monitor the temperature of the oil sample and adjust the heating block/bath thermostat, if necessary. Observe the temperature of the oil sample twice during the first hour, then once every hour for at least 3 h, making the necessary adjustment each time until a constant temperature of 120 +/- 1°C is read twice in succession. Check the air flow and temperature at least twice a day and adjust the control flow, when necessary.

10.8 At the end of 312 h (13 days), remove the oxidation cell containing the oxidized oil and delivery tube from the bath or block, and allow the oxidized oil to cool to room temperature. When an oil bath is used, rinse the outside of the oxidation cell with heptane and wipe dry. Place the cell and its contents in a tared 1000-mL beaker and obtain the weight of the oil sample, oxidation cell, and delivery tube as in 10.4. Record this weight, A1.

10.9 Weigh a 2.8-µm glass fiber filter to the nearest 0.01 g and record, F1. Using the filter holder apparatus, vacuum filter the cooled oxidized oil through the glass filter. Determine the viscosity at 100°C of the filtered oil by Test Method D445. Record the viscosity result, V1.

NOTE 4 - The viscosity and sludge determinations for the oxidized oil should be done within four days after removing the cell from the heating bath or block. It has been found that extending storage time beyond four days can give variable test results.

10.10 Wash the oxidation cell and air delivery tube with heptane and filter the washings through the same filter. Continue washing until the heptane is no longer colored by the oxidized oil. Draw air through the filter until the precipitate appears dry. Place the filter in an operating hood for 0.5 h to evaporate heptane. Transfer the filter to a 50 to 60°C explosive-proof oven for 0.5 h. Let cool to room temperature and weigh, F2.

10.11 Allow heptane to evaporate from the oxidation cell and then place the cell in an explosive-proof oven at 50 to 60°C for 1 to 2 h. Dry the air delivery tube by passing air through the tube. Let the oxidation cell cool to room temperature. Weigh the oxidation cell and air delivery tube, B2.

11. Calculations
11.1 Determine the amount of sludge, viscosity change, and oil loss by the following equations.
11.1.1 Filterable sludge on filter, g.
D2 = F2 - F1
where:
D2 = amount of sludge on filter pad, g,
F2 = weight of filter pad and sludge, g, and
F1 = weight of filter, g.

11.1.2 Adherent sludge on oxidation cell and air delivery tube, g.
D1 = B2 - B1
where:
D1 = amount of sludge on oxidation cell and air delivery tube, g,
B2 = weight of oxidation cell and air delivery tube, solvent washed and dried, g, and
B1 = original weight of oxidation cell and air delivery tube, g.

11.1.3 Total sludge, g.
D3 = D1 + D2
where:
D3 = total amount of sludge, g.

11.1.4 Viscosity at 100°C increase, mm2, %
V3 = (V1 - V2)/V2 x 100
where:
V3 = viscosity increase, %,
V2 = original viscosity of oil sample, and
V1 = viscosity of oxidized oil sample.

11.1.5 Oil loss, g.
C3 = A2 - A1
where:
C3 = oil loss, g,
A2 = original combined weight of oil sample, oxidation cell, and air delivery tube, g, and
A1 = combined weight of oxidized oil, oxidation cell, and air delivery tube, g.