ASTM D873 Oxidation Stability of Aviation Fuels (Potential Residue Method)
10. Procedure
10.1 Bring the pressure vessel and the fuel to be tested to a temperature from 15 to 25°C. Place the weighed glass sample container in the pressure vessel and add 100 +/- 1 mL of test specimen. Alternatively, transfer 100 +/- 1 mL of sample into the weighed glass sample container first, before placing the glass sample container into the pressure vessel. Cover the same container, close the pressure vessel, and using a quick release coupling, introduce oxygen until a pressure from 690 to 705 kPa is attained. Allow the gas in the pressure vessel to escape slowly through the needle valve at a rate not to exceed 345 kPa/min. Repeat the charging and exhausting of the oxygen once more in order to flush out the air originally present. Introduce oxygen again until a pressure of from 690 to 705 kPa is attained and observe for leaks, ignoring an initial rapid drop in pressure (generally not over 40 kPa), which can be observed because of the solution of oxygen in the sample. Assume the absence of leaks, and proceed with the test if the rate of pressure drop does not exceed 15 kPa in 10 min.
10.2 Place the charged pressure vessel in one of the described oxidation baths, being careful to avoid shaking, and record the time of immersion as the starting time. Leave the pressure vessel in the oxidation bath for the specified "X" hour aging time. If the temperature at the start of a test varies from 100°C, adjust the "X" hour aging time by the correction factors given in Table 1.
10.3 At the completion of the period of oxidation, remove the pressure vessel from the bath. To minimize further oxidation of the test specimen and to provide for safe venting of the pressure vessel, cool the pressure vessel to approximately room temperature within 30 min after removal from the bath, using water not more than 35°C. Release the pressure slowly through the needle valve at a rate not to exceed 345 kPa/min. Take the pressure vessel apart, and remove the sample container.
10.4 Transfer the oxidized fuel from the glass sample container to a graduated flask, such as a graduated, stoppered cylinder, that will allow mixing of approximately 120 mL, if no visible precipitate is observed or if the amount is not specifically required by specifications. Wash the interior of the glass sample container twice with 10-mL portions of gum solvent to remove any gum. Mix the oxidized fuel and rinses thoroughly, and preserve the mixture for the determination of soluble gum. Proceed with the test as specified in 10.6. If a precipitate is observed, and if the amount is required by specifications, filter the oxidized fuel through a sintered-glass crucible of fine porosity and save the filtrate. Wash the interior of the glass container twice with 10-mL portions of gum solvent to remove any gum or precipitate. Filter the washings through the crucible, adding them to the oxidized fuel filtrate, and mix thoroughly. Preserve the mixture for the determination of soluble gum.
10.5 Dry the crucible in an oven maintained at 100 to 150°C for 1 h, cool in a cooling vessel to approximately room temperature (for at least 2 h), and weigh. Record any increase in mass as precipitate, A.
10.6 Dry the glass sample container in an oven maintained at 100 to 150°C for 1 h, cool in a cooling vessel, and weigh. Two hours has been found to be a suitable time to cool the glass sample container. Record any increase in mass as insoluble gum, B.
10.7 Divide the mixture obtained in 10.4 into two equal portions (within 2 mL), and determine the soluble gum existing therein by the procedure and test conditions described in Test Method D381, using in each test the entire half portion instead of the 50-mL test specimen specified in Test Method D381. Record the sum of the increase in mass of the two beakers as soluble gum, C, as calculated in accordanve with the following equation:
C = 1000 x (D - E) + (F - G) + 2(X - Y)
where:
C = soluble gum, mg/100 mL,
D = mass of test specimen beaker 1 + residue, g,
E = mass of test specimen beaker 1, g,
F = mass of test specimen beaker 2 + residue, g,
G = mass of test specimen beaker 2, g,
X = mass of tare beaker (before), g, and
Y = mass of tare beaker (after), g.
