ASTM D893 Standard Test Method for Insolubles In Used Lubricating Oils
9. Procedure A for Pentane and Toluene Insolubles Without Coagulant
Pentane Insolubles
9.1 Dry a clean centrifuge tube for 30 min at 105 +/- 3°C, cool in a desiccator, and weigh to the nearest 1 mg. Weigh 10.0 +/- 0.1 g of the prepared sample of used oil into the tube and fill to the 100-mL mark with pentane (Warning - See Note 5). Stopper the tube and shake until the mixture is homogeneous. Do not allow the mixture to stand more than 3 h.
9.2 Remove the stopper, and using a wash bottle having a fine jet, wash all insolubles from the stopper into the centrifuge tube with a minimum of pentane. Balance the weights of each pair of filled centrifuge tubes, place them in the centrifuge on opposite sides of the head, and centrifuge for 20 +/- 1 min at a rate calculated in accordance with 6.2, sufficient to produce a relative centrifugal force (rcf) between 600 and 700 at the tips of the whirling tubes. (See Table 2.) Carefully decant the supernatant liquid without disturbing or dispersing the precipitate, leaving not more than 3 mL of liquid in the centrifuge tube.
9.3 Add 10 +/- 1 mL of pentane to the tube. Dislodge and break up all of the insolubles from the bottom of the tube by means of a clean stiff wire. Wash all insolubles adhering to the wire back into the tube with pentane, filling the tube to the 50-mL mark. Stopper the tube and shake until the mixture is homogeneous. Remove and wash the stopper. Centrifuge for 20 +/- 1 min. Pour the supernatant liquid from the centrifuge tube, using care to avoid disturbing the cake of insolubles in the bottom of the tube.
9.4 Repeat the entire operation described in 9.3.
9.5 Dry the centrifuge tube containing the washed precipitate for 30 min at 105 +/- 3°C, cool in desiccator, and weigh to the nearest 1 mg.
9.6 With relatively heavy precipitates there can be some spattering if the tube is placed directly from the centrifuge into the oven. In such cases, the precipitate may be partially dried by weathering at room or slightly higher temperatures before being placed in the oven.
Toluene Insolubles
9.7 Starting with a fresh sample of used oil, precipitate and centrifuge the pentane insolubles as described in 9.1-9.4, but do not dry the insolubles in the centrifuge tube.
9.8 Add 10 +/- 1 mL of toluene-alcohol solution (See Note 2 and Note 3). Break up and dislodge all of the insolubles from the bottom of the centrifuge tube by means of a clean, stiff wire. Wash any insolubles adhering to the wire back into the tube with toluene-alcohol solution, using a sufficient amount of this solvent to fill the tube to the 50-mL mark. Stopper the tube and shake until the mixture is homogeneous. Remove the stopper and wash the adhering insolubles back into the tube with a minimum amount of toluene. Centrifuge until no visible insolubles remain in suspension in the solvent; 10 to 20 min are usually sufficient. Decant the clear solution, taking care not to disturb the precipitate.
9.9 Repeat the washing procedure described in 9.7, substituting toluene for the toluene-alcohol solution.
9.10 Dry for 1 h at 105 +/- 3°C (Note 3), cool in a desiccator, and weigh to the nearest 1 mg.
10. Procedure B for Coagulated Pentane and Toluene Insolubles
10.1 Coagulated Pentane Insolubles - Proceed in accordance with 9.1 and 9.2, except in 9.1 use pentane-coagulant solution (7.9) in place of pentane. Wash the precipitate twice with pentane, dry and weigh as directed in 9.3, 9.4, and 9.5.
10.2 If the sample is known to contain water, or if water is indicated by a gummy precipitate, repeat the determination on a sample that has been dried by heating to 105 +/- 3°C in an open beaker.
10.3 Coagulated Toluene Insolubles - Proceed in accordance with 9.1 and 9.2 except in 9.1 use pentane-coagulant solution (7.9) in place of pentane. Wash twice with pentane as directed in 9.3 and 9.4. Wash with toluene-alcohol solution and toluene, dry, and weigh as directed in 9.7-9.9.
11. Calculation
11.1 Calculate the percentage of insolubles in the used oil as follows:
Insolubles, % = 10 (B - A)
where:
A = mass of clean, dried, centrifuge tube, g, and
B = mass of dried insolubles and centrifuge tube, g.
